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Revista Colombiana de Obstetricia y Ginecología logoLink to Revista Colombiana de Obstetricia y Ginecología
. 2026 Jan 17;76(4):4268. doi: 10.18597/rcog.4268

Effectiveness of treating gestational syphilis in the last trimester on the incidence of congenital syphilis: a systematic review and meta-analysis

Efectividad del tratamiento de la sífilis gestacional en el último trimestre sobre la incidencia de sífilis congénita: revisión sistemática y metanálisis

Ana María Gutiérrez-Tamayo 1, Leidy Viviana Mirama-Calderón 1, María Teresa Vallejo-Ortega 2,3,*, Hernando Guillermo Gaitán-Duarte 4
PMCID: PMC12947668  PMID: 41671009

ABSTRACT

Objectives:

To evaluate the effectiveness and safety of treatment for gestational syphilis during the third trimester on maternal and perinatal outcomes, according to the timing of administration relative to delivery, and assess the certainty of the body of evidence.

Materials and methods:

This systematic review included randomized controlled trials, quasiexperimental studies, cohort studies, and case series involving women diagnosed with GS at 28 weeks’ gestation or later, treated with penicillin or other antibiotics. Search was done in 2023 and updated on June 2025. Two researchers selected studies and extracted data. We assessed the incidence of Congenital Syphilis and maternal treatment failure. Outcomes are presented by maternal and perinatal endpoints and treatment regimen.

Results:

No randomized controlled trials were identified. Ten cohort studies comprising 5438 women with GS and three case series of Congenital Syphilis were included. Benzathine penicillin G administered during the third trimester might be associated with a cumulative incidence of Congenital Syphilis of 8% (95% CI: 2-13%). The effectiveness of treatment administered 4 weeks before delivery remains uncertain. Aminopenicillins were possibly associated with a 43% incidence of Congenital Syphilis. Safety data were limited. Case series of foetuses with hidrops fetalis associated with gestational syphilis to mothers treated with a 10-day course of intravenous aqueous crystalline penicillin G showed seven newborns with complete response, suggesting prevention of Congenital Syphilis.

Conclusion:

Treatment of GS with benzathine penicillin G during the third trimester is beneficial in reducing the risk of Congenital Syphilis. However, as its effectiveness is uncertain when administered fewer than 30 days before delivery, neonates born within this timeframe should continue to be managed in accordance with current guidelines for possible Congenital Syphilis. Aminopenicillins may be associated with a high rate of treatment failure. Alternative strategies to treat the fetus during the final four weeks of pregnancy are needed to reduce the risk of Congenital Syphilis.

Keywords: Syphilis, congenital syphilis, treponema pallidum, pregnant women, penicillins, macrolides, ampicillin, therapeutics

INTRODUCTION

Syphilis is an infection caused by the bacterium Treponema pallidum (TP), transmitted through sexual contact, transplacental passage, or blood transfusion 1. Its incidence has increased globally, particularly in Latin America and Africa 2. Gestational syphilis (GS) refers to infection acquired during pregnancy or the presence of an untreated preexisting infection in a pregnant woman. TP can cross the placenta from the end of the first trimester onwards 3. Vertical transmission may be asymptomatic or result in adverse outcomes including intrauterine death, preterm birth, or neonatal sepsis 4. Infants infected in utero are diagnosed with congenital syphilis (CS). Timely diagnosis and treatment of gestational syphilis can prevent or cure CS 5. Failures in prevention are often associated with lack of access to, or nonattendance at, antenatal care 6.

Penicillin remains the standard treatment for syphilis, GS, and CS 4. Given that TP divides approximately every 30 hours 7, effective bactericidal activity in early syphilis requires penicillin concentrations to remain above 0.03 IU/ mL (18 ng/mL) for 7-10 days without interruption exceeding 24 hours 8. In late syphilis, due to slower bacterial replication, a longer duration of treatment is necessary to maintain adequate therapeutic levels 8.

The generic name of the antibiotic is benzylpenicillin or penicillin G. It is available as an aqueous solution for parenteral use specifically, aqueous crystalline penicillin G. This formulation has a rapid onset and a short half-life (30-60 minutes), necessitating frequent intravenous administration. It crosses the blood-brain barrier in the presence of inflammation and achieves effective transplacental passage 9, making it the treatment of choice for neurosyphilis and CS 4. Depot formulations such as procaine penicillin and benzathine penicillin G are also available. Procaine penicillin comprises penicillin and procaine in equimolar concentrations, resulting in slower absorption when administered intramuscularly every 8-12 hours 10. Benzathine penicillin G, formed by combining penicillin G with diphenylethylenediamine, has a half-life of approximately seven days and is also administered intramuscularly 8. Benzathine penicillin G is indicated for the treatment of early syphilis (single dose) and late syphilis (three weekly doses) 4, based on its pharmacokinetic requiring fewer doses. Although aqueous crystal-line penicillin G has been used to treat gestational syphilis since 1949 11, current practice typically involves the use of benzathine penicillin G in the same regimen as for non-pregnant women 4.

Alexander et al. reported that a single dose of 2.4 million units of benzathine penicillin G administered to pregnant women with syphilis cured 98% of CS cases 12. Notably, four of the six CS cases occurred in neonates born within two weeks of maternal treatment. These findings appear to support current guideline recommendations which consider neonates born to mothers treated less than 30 days prior to delivery as possibly infected and in need of additional treatment 4,13,14.

Given that a substantial proportion of women are diagnosed with syphilis during the third trimester 15,16, and that partner treatment is often inadequate resulting in a heightened risk of maternal reinfection later in pregnancy 17,18 it is essential to appraise the evidence supporting the classification of treatment as inadequate if administered within 30 days of delivery. This recommendation leads to neonates undergoing a 10-14 day course of intravenous aqueous crystalline penicillin G 4, which may increase the risk of adverse events associated with intravenous therapy and prolonged hospital stays, particularly among preterm neonates 19. Likewise, it is relevant to answer the question about the risk of congenital syphilis occurring within the last twelve weeks, and more specifically within the final four weeks of pregnancy, among women who receive standard treatment with benzathine penicillin G or alternative regimens.

This systematic review therefore aims to assess the effectiveness and safety of treatment for gestational syphilis during the third trimester on maternal and perinatal outcomes, with specific reference to the timing of administration relative to delivery and the certainty of the available evidence.

METHODS

Design

Systematic Review. The protocol was the degree work to obtain the title of specialist in Obstetrics and Gynecology at the National University of Colombia (see the registered document at the university in November, 2023 Supplementary Appendix 1). This manuscript follows the recommendations of the PRISMA statements to report Systematic Reviews.

graphic file with name 2463-0225-rcog-76-04-4268-gf4.jpg

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Eligibility Criteria

This systematic review included randomized controlled trials, quasi-experimental studies, cohort studies, and case series available in full text. Eligible studies involved women with a confirmed diagnosis of gestational syphilis or women with suspected or confirmed reinfection, previously untreated, at 28 weeks’ gestation or beyond, who received antibiotic treatment with penicillin or other antibiotics (β-lactams or macrolides) with or without a comparison group. We excluded studies that did not report data specific to this gestational age group. Studies published in Spanish, English and Protuguese, between 1999 and 2025 were searched, based on the adoption of the term “inadequately treated” in the 2005 CDC guidelines, which referred to treatment administered fewer than four weeks before delivery 20.

Search strategy and databases

Searches were conducted by a specialist of the former STI Cochrane Group, in MEDLINE, EMBASE, and CENTRAL (see Supplementary Appendix 2), The strategy combined controlled vocabulary and freetext terms for “Syphilis”, “Pregnancy”, “Penicillins”, “Cephalosporines”, and related concepts. Syntax was refined using field codes, proximity operators and Boolean operators. Additionally, a snowballing technique was used to identify further relevant references. The initial search was performed in December 2023 and updated in June 2025. References were managed and de-duplicated using EndNote®.

Search electronic report #1
Database Ovid MEDLINE ALL(R) / PubMed(R) 1946 to Present
Platform Ovid
Search Date 30/Jun/2025
Range of search date None
Language restrictions None
Other limits None
Search strategy (results)
  1. exp Syphilis/ (30643)
  2. exp Syphilis, Latent/ (643)
  3. exp Syphilis, Congenital/ (3209)
  4. exp Syphilis Serodiagnosis/ (5978)
  5. exp Treponema pallidum/ (4763)
  6. syphilis.tw (30421)
  7. lues.tw (509)
  8. (treponema adj1 pallidum).tw (5318)
  9. (great adj1 pox).tw (12)
  10. (hutchinson$ adj1 teeth).tw (14)
  11. or/1-10 (44190)
  12. exp Pregnancy/ (1062441)
  13. exp Pregnant People/ (16844)
  14. pregnan$.tw (647967)
  15. gestat$.tw (272371)
  16. gravid$.tw (17812)
  17. or/12-16 (1288526)
  18. 11 and 17 (4467)
  19. exp Penicillins/ (87157)
  20. exp Penicillin G/ (42901)
  21. exp Penicillin G Benzathine/ (2043)
  22. penicil?in$.tw (64356)
  23. benzylpenicillin$.tw. (2727)
  24. benzathine.tw (1301)
  25. ampicillin.tw (28999)
  26. exp Cephalosporins/ (48534)
  27. cephalospor$.tw. (28270)
  28. exp Cefotaxime/ (13574)
  29. cephotaxim$.tw (67)
  30. cefotaxim$.tw (10580)
  31. exp Ceftriaxone/ (7229)
  32. ceftriaxon*.tw. (15302)
  33. exp Macrolides/ (126911)
  34. macrolide$.tw (20712)
  35. exp Erythromycin/ (28966)
  36. erythromycin$.tw (24528)
  37. exp Azithromycin/ (7361)
  38. azithromycin$.tw (13160)
  39. exp Clarithromycin/ (7329)
  40. clarithromycin.tw (11416)
  41. exp Probenecid/ (3637)
  42. probenecid.tw (4042)
  43. or/19-42 (329724)
  44. 18 and 43 (716)
# of records identified 716
# of records without duplicates 457
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Screening and data extraction.

Two of three reviewers (AG, VM, and MTV) independently screened titles, abstracts, and full texts, and extracted data. Discrepancies were resolved by a fourth reviewer (HG). We used Rayyan software 21 to facilitate the screening process. Full texts of potentially eligible studies were reviewed to confirm inclusion and rule out exclusion criteria. Extracted data included study characteristics (design, sample size calculation, funding), population characteristics (trimester at diagnosis, gestational syphilis confirmation method, infection stage), treatment details (type of antibiotic, number treated, definitions of adequate/inadequate or complete/incomplete treatment, timing of administration relative to delivery), and outcomes.

Risk of bias assessment.

We consider to use the ROB II tool 22 for RCTs and the ROBINS-I tool 23 for quasiexperimental and controlled cohort studies. Uncontrolled cohort studies were assessed using a tool, developed by our team, to assess the risk of bias in series of subjects exposed to an intervention (see Supplementary Appendix 3). Case series were evaluated using the Joanna Briggs Institute checklist 24.

Checklist for series of subjects exposed to intervention studies
Reference:
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
Selection Does the study define an appropriate, clear, and focused research question? Yes
No
Unclear
Selection
1.2 Is there a clear description of the inclusion criteria for subjects exposed to the intervention? Yes
No
Unclear
1.3 Is there a clear description of the exclusion criteria for subjects exposed to the intervention? Yes
No
Unclear
1.4 Is clear the proportion of eligible subjects who participated in the study? (Describe the proportion, please ) Yes
No
Unclear
1.5 Were exposed subjects included in strict sequential order? Yes
No
Unclear
Measurement
1.6 Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention? Yes
No
Unclear
1.7 Is the intervention applied to the subjects clearly defined? Yes
No
Unclear
1.8 Is the level to exposition to intervention described in detail (adherence measurement)? Yes
No
Unclear
1.9 Were any co-interventions applied differentially to the exposed subjects? Yes
No
Unclear
1,10 Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment? Yes
No
Unclear
1.11 Are prognostic variables adequately defined and measured? Yes
No
Unclear
1.12 Are outcome variables adequately defined and measured? Yes
No
Unclear
Atrittion
1.13 Is there a description of proportion of subjects were lost to follow-up? Yes
No
Unclear
Confounding
1.14 Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)? Yes
NO
Unclear
Other problems
1.15 Is there an estimation of the required sample size to determine the benefit of the intervention? Yes
NO
Unclear
1.16 Are confidence intervals for the absolute effect of the intervention presented Yes
NO
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Considering clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes
NO
Unclear
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes
NO
Unclear
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GETS: Grupo de Evaluación de Tecnologías y Políticas en Salud.

Assessment instruction

Outcomes measured

Incidence of Congenital Syphilis, poor fetal outcomes, and maternal treatment failure (i.e., no serological titre decline post-treatment). Safety outcomes included systemic allergic reactions and Jarisch-Herxheimer reactions.

Data synthesis and statistical analysis.

Effects of treatment are presented as CS incidence of by study type, outcome, and antibiotic used. Subgroup analyses were conducted based on time from treatment to delivery and treatment adequacy. The mother was the unit of analysis for treatment, and the foetus or neonate for outcomes. Incidence of Congenital Syphilis was pooled using meta-analysis of cumulative incidences, applying the direct method with a random-effects model 25. Where heterogeneity was high, we reported the range of estimates. Heterogeneity was assessed visually and using the I2 statistic.

Certainty of evidence. The certainty of the evidence was evaluated using the GRADE approach, considering risk of bias, inconsistency, directness, imprecision, and other factors. For observational studies, upgrading was considered when large effect sizes, dose-response relationships, or bias toward the null with consistent effect direction were present 26.

RESULTS

Screening and selection of studies

A total of 1,894 records were identified, of which 289 were excluded as duplicates. The remaining 1,605 titles and abstracts were screened for eligibility. Ninety-six articles were assessed in full text; of these, 53 did not meet the inclusion criteria, 19 were excluded due to language restrictions (Chinese: n=16; German: n=2; Polish: n=1), nine did not report data specific to women in the third trimester, and two were unavailable (see ultimately included: ten cohort studies 12,27-35 Supplementary Appendix 4). Thirteen studies were and three case series 36-38 (Figure 1).

Reference Reason for exclusion
Alberto C, Wagner N, Fougère Y, Meyer Sauteur PM, Scherler G, Aebbi-Popp K, et al. Syphilis in pregnant women and congenital syphilis from 2012 to 2021 in Switzerland: a multicentre, retrospective study. Swiss Medical Weekly. 2024;154(11). No 3rd trimester data available
Gao J, Chen X, Yang M, Wu Y, Liang T, Li H, et al. Adverse pregnancy outcomes and associated risk, factors among pregnant women with syphilis during 2013-2 018 in Hunan, China. Frontiers in Medicine. 2023;10. No 3rd trimester data available
Iroha K, Masashi D, Kenji T, Yutoku S, Akiko U, Tokuro S, et al. Case report of fourteen pregnant women with syphilis. Journal of Obstetrics and Gynaecology Research. 2023;49(1):447. Full text not retrieved
Johnson KA, Burghardt NO, Snyder RE, Plotzker RE, Imp BM, Murphy R, et al. Comparing 7-Day Versus 6-8-Day Penicillin Treatment Intervals Among Pregnant People With Syphilis of Late or Unknown Duration: No Difference Found in Incidence of Congenital Syphilis. Open Forum Infectious Diseases. 2023;10(6). No 3rd trimester data available
Liu H, Chen N, Tang W Shen S, Yu J, Xiao H, et al. Factors influencing treatment status of syphilis among pregnant women: a retrospective cohort study in Guangzhou, China. International Journal for Equity in Health. 2023;22(1). No 3rd trimester data available
Mo XF, Feng MZ, Jiang TT, Xu YT, Wu MJ, Li JJ, et al. Treatment of maternal syphilis for preventing congenital syphilis: an observational study of adherence to treatment recommendation in Suzhou, China, 2019-2021. Sexual Health. 2023;20(6):523-30. Full text not retrieved
Patil S, Li X, Liu P Dai Y, Zhu X, Li J, et al. A Retrospective Cohort Study on Treponema pallidum Infection: Clinical Trends and Treatment Outcomes for Congenital Syphilis in Guangxi, China (2013-2023). Infection and Drug Resistance. 2024;17:2351-9. No 3rd trimester data available
Sangtawesin V, Lertsutthiwong W Kanjanapattanakul W Khorana M, Horpaopan S. Outcome of maternal syphilis at Rajavithi Hospital on offsprings. Journal of the Medical Association of Thailand. 2005;88(11):1519-25. (“Randomized C
Sayal HB, Yavuz A, Tsakir B, Toprak, E, Han O, Inal H. Maternal and neonatal outcomes of congenital syphilis at a tertiary care center in Turkey; a retrospective observational study. Journal of Obstetrics and Gynaecology. 2024;44(1). No 3rd trimester data available
Tannis A, Miele K, Carlson JM, O'Callaghan KP Woodworth KR, Anderson B, et al. Syphilis Treatment among People Who Are Pregnant in Six U.S. States, 2018-2021. Obstetrics and Gynecology. 2024;143(6):718-29. No 3rd trimester data available
Wang H, Ying X, Lin D, Uwimana MMP Zhang X. Towards the elimination of mother to child transmission of syphilis 2015-2020: practice and progress in Zhejiang province, eastern China. BMC Pregnancy and Childbirth. 2023;23(1). No 3rd trimester data available
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Figure 1. Flowchart of studies.

Figure 1

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Source: Authors.

Study characteristics

Eight of the ten cohort studies were retrospective, four were from China 27,28,32,34, and one each from the United States 12, Japan 30, Thailand 29, and Tanzania 33. Three of the ten were cohorts with control group (not treated) 28,32,34. Data sources included hospital records 12,29,30,33, administrative databases or information systems 27,28,32,34, and public health program records 31,35. The case series were conducted in the United States 36, Colombia 37, and Thailand 38. None of the included studies received industry funding.

The cohort studies collectively included 5,438 pregnant women diagnosed with syphilis in the third trimester, along with their respective foetuses. Diagnosis of maternal syphilis was based on a positive non-treponemal test confirmed by a treponemal test, with one study using the reverse algorithm 29. The stage of maternal syphilis at diagnosis was not reported in three studies 28,33,34 (Table 1). All studies diagnosed congenital syphilis neonatally, using between two and five clinical and paraclinical criteria. (Table 2).

Table 1. Baseline characteristics of women with gestational syphilis who have received treatment in the last trimester of pregnancy.

Author Country Year of the study Type of study Population third quarter Diagnosis Syphilis stage Time between treatment and delivery
Alexander, J. et al 12 1999 United States 1987-1989 Retrospective cohort based on hospital population 77 VDRL o RPR / Treponemal Primary Secondary Early latent, late < 12 w†
Dou et al 27 2016 China 2013 Retrospective cohort based on administrative data 1966 Positive Treponemal and not treponemal test Primary, Secondary, Early or late latent < 12 w
Hong, F. et al 28 2017 China 2003-2014 Retrospective cohort Based on administrative data 551 TRUST / TTPA Uninformed <12 w ‡
Luengmettakul et al 29 2025 Thailand 2015-2021 Retrospective cohort based on hospital population 104 RPR/TPHA before 2017 Inverse algorithm after 2017 Primary, Secondary, Early or late latent < 12 w
Nishijima, T et al 30 2020 Japan 2010-2018 Retrospective cohort based on hospital population 14 RPR Primary Secondary Early latent, late latent and unknown duration < 8 w
Qin JB, et al 31 2013 China 2007 - 2012 Prospective cohort (Public health program) 143 TRUST / TPPA Early, latent, late <10 w
Wan et.al. 32 2020 China 2013-2019 Retrospective cohort based on information system 1234 RPR or TRUST / TPPA or ELISA Primary, secondary, tertiary or latent.
Watson- Jones, D. et al 33 2002 Tanzania 1997-1999 Retrospective cohort based on hospital population 99 RPR/ Treponemal Uninformed < 12 w$
Zhang X et al 34 2016 China 2013-2014 Retrospective cohort based on administrative data 737 TRUST - RPR/ TPHA Uninformed < 12 w*
Zhu et al 35 2010 China 2002-2006 Prospective cohort (Public health program) 630 RPR/ TPHA Primary, Secondary, Early and late Latent, < 12 w*
Camacho et al 36 2021 Colombia 2016-2020 Case series 4 new-borns Quantitative VDRL and hidrops fetalis NA >28 weeks (3 cases)
Sheffield J, et al. 37 2002 United States 1992-1998 Case series 43 newborns Quantitative VDRL -RPR NA >37 weeks (65%)
Yanase et al. 38 2025 Thailand 2024-2025 Case series 5 new-borns Quantitative VDRL/placenta ( 1 case) Hidrops fetalis NA >26 weeks (4 cases) >28 weeks (1case)
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Rapid plasma reagin (RPR), Treponema pallidum hemagglutination (TPHA), Treponema pallidum particle agglutination (TPPA), Toluidine red unheated serum test (TRUST)

* Pregnant women over 28 weeks of age were included

† The mean gestational age at the time of syphilis treatment and at the time of delivery was 32.75 + 6.73 and 38.60 + 1.57 weeks respectively.

‡ Pregnant women over 30 weeks of age were included

§ Pregnant women over 32 weeks of age were included

Venereal Disease Research Laboratory (VDRL)

** The number of patients who received Penicillin at third trimester

Source: Authors.

Table 2. Effectiveness and safety of antibiotics for treating gestational syphilis in the last trimester. Maternal and perinatal outcomes.

Study Type of treatment Diagnosis of CS CS incidence (95%CI) Last 4 weeks (95%CI) Maternal treatment failure (95%CI) Adverse events incidence (95%CI)
Alexander, J. et al. (12) 1999 Benzathine penicillin G

1. Abnormal physical examination consistent with CS

2. NTT 4-fold higher than mother at delivery

3. Placenta with syphilis infection

 4/77 - (5.2%) (1.4% to 12.8%)a 2/31 6.5% (0.8% to 21.4%) 1/77 1.3% CI (0.1 - 6.2)b -
Dou et al (27) 2016 Benzathine penicillin G or procaine penicillin

1. Postitive TT and NTT 4-fold higher than mother at delivery

2. IGM positive for Tp

3. To in dark-field microscopy

 67/1966 - 3.4% (2.7% to 4.3%) NRg - -
Untreated + treated after 37 weeks 341/8795 - 3.97 (3.50-4.30)
Hong, F. et al (28) 2017 Benzathine penicillin G or procaine penicillin

1. NTT 4-fold higher than mother at delivery

2 A four-fold or greater rise in NTT titre during the follow-up

3. A reactive 19S-IgM-TPPA

4 A reactive NTT that did not revert to nonreactive by end of 18 months’ follow-up

 11/551 - 2.15% (1.1% to 3.8%)
No treated 141/1153 - 12.23% (10.4% to 14.3%) - - -
Lueng- mettakul et al (29) 2025 Benzathine penicillin G

1. Abnormal physical examination con- sistent with CS

2. NTT 4-fold higher than mother at delivery

3. Placenta with syphilis infection

 NRh NRh - -
Nishijima, T. et al (30) 2020 Aminopenicillins

1. Serum NTT titer >4-fold that of the mother’s

2. (FTA-ABS) test result positive for serum IgM

3. Lesion tissue or body fluid samples positive by PCR

4 lesion or fluid samples positive for T. p on dark field microscopy

5. Abnormal physical examination consistent with CS

 6/14 - 42.9% (19.6% to 68.9%)f - 2/14 14.3% (1.8% to 42.8%) 3/14 21.4% (4.7 % to 50.8%)
Qin JB, et al (31) (2014) Benzathine penicillin G

1. A positive dark-field or fluorescent antibody test of body fluid

2. Abnormal physical examination consistent with CS and NTT 4-fold higher than mother at delivery

3. FTA-ABS 19S IgM test

4. A reactive NTT test 18 months after birth

 26/143 - 18.2% d (12.2% to 25.5%) 30/128 - 23.4% (16.4% to 31.7%) - -
Wan Z et al (32) 2020 Penicillin, not specified

1. Postitive TT and Non TT 4-fold higher than mother at delivery

2. IGM positive for Tp

3. To in dark-field microscopy

 34/1234 - 2.8% (1.9% to 3.8%) - -
No treated 30/1364 - 2.2% (1.5% to 3.1%) - - -
Watson- Jones, D. et al (33) 2002 Benzathine penicillin G - - - - -
Zhang X et al (34) 2016 Benzathine penicillin G or procaine penicillin

1. Serum NTT titer >4-fold that of the mother’s

2. Abnormal physical examination consistent with CS

3. positive Non TT tests lasting until 18 months after birth Infants with positive IgM Treatment to mother less than 30 days to delivery

 19/737 - 2.6% (1.6% to 4%) - - -
No treated 28/745 -3.8% (2.5% to 5.4%) - - -
Zhu et al (35) (2010) Benzathine peni- cillin G (2 dose for early- 3 dose for late) 1. Congenital syphilis is syphilis in an infant whose mother has transmitted the infection vertically to the fetus 175/630 -27.8% (24.3% to 31.5%)d - - -
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95%CI: 95%Confidence Interval

The 95% confidence interval was estimated by the authors of the SR as it is not contained in the manuscripts of the included studies.

CS: Congenital syphilis TT : treponemal Tests. NTT No trponemal test

a. Women from 30 - 42 weeks of GA were included. However, women from 26 - 30 of GA were also included. Taking into account this group CS cumulative incidence was 3.7%. 4/6 cases were treated in the last 2 weeks of pregnancy

b. One woman was HIV infected

c. Prematurity by Ultrasound or LMP. Dubovitz was also performed. With this test prematurity incidence was 5.8%. Poor pregnancy outcomes were 28,5% in high- titer active syphilis and 18,1 for low-titer active syphilis

d. Data were not adjusted by complete or incomplete treatment (25%)

e. The denominator combines treated and untreated women for GS

f. Women initiating treatment < 60 days before delivery were analysed. Women treated > 60 days CS cumulative incidence was 14%

g. NR: Data published not reported because the proportions included untreated women.

h. The authors combined untreated women with those treated fewer than 30 days before delivery, as well as women who received an incomplete treatment regimen prior to delivery. Among women treated after 28 weeks’ gestation, the study reported a congenital syphilis incidence of 23 out of 104 cases; however, the cumulative incidence of congenital syphilis is not reported consistently throughout the publication.

Source: Authors.

Risk of bias assessment

All cohort studies were assessed as having a very high risk of bias (two or more domains rated as high risk) (Figure 2 and Supplementary Appendix 5). None of the studies reported a sample size calculation. The case series scored 6/10 (37), 7/10 (36), and 9/10 (38) on the Joanna Briggs Institute checklist (Supplementary Appendix 5).

Figure 2. Risk of bias in cohorts without control assessing use of antibiotics gestational syphilis in the last trimester of pregnancy.

Figure 2

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Source: Authors.

Checklist for series of subjects exposed to intervention studies
Reference: Alexander JM, Sheffield JS, Sanchez PJ, Mayfield J, Wendel GD Jr. Efficacy of treatment for syphilis in pregnancy Obstet Gynecol. 1999 Jan;93(1):5-8. doi: 10.1016/s0029- 7844(98)00338-x
Checklist verified by: HGD, AMGT
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

“To evaluate the efficacy of the CDC recommendations for the treatment of syphilis in pregnancy for the eradication of maternal infection and prevention of congenital syphilis.”

Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

“Rapid plasma reagin test, VDRL test with titer and con®rmatory microhemagglutinin assay for antibodies to Treponema pallidum were used to identify infected patients.”

Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

There is no information

 Yes
No
Unclear X
1.4

What proportion of eligible subjects participated in the study?

340/340 (100%)

 Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

It looks like yes

 Yes
No
Unclear X
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

There is not information

 Yes
No X
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

Four hundred forty-eight women (1.6% of the population) had untreated syphilis, of those 340 (75.9%) received prenatal care and antepartum therapy””

Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Primary, secondary or early latent (under 1 year duration) syphilis was treated with 2,400,000 units intramuscular (IM) benzathine penicillin G. Late latent syphilis (uncertain or longer than 1 year duration) was treated with 7,200,000 units IM benzathine penicillin G over 3 consecutive weeks

 Yes X
No
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is not information

 Properly treated
Unproperly treated
It is not clear X
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open-label study Hard outcome. Measured with non-treponemal test titers for the mother and complete serological and clinical examination of the new-born and isolation of confirmed tp.

Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

There is not information

 Yes
No X
Unclear
1.12

Are outcome variables adequately defined and measured?

For GS. Clinical cure was defined by the resolution of symptoms in patients with primary or secondary syphilis and a fourfold decrease in titer over 3±4 months. In patients with latent syphilis, a fourfold decrease in titer over 6 months was considered a clinical cure. Treatment failure was defined as a persistent (longer than 1 month) fourfold increase in titer, or an unchanged titer 6 months after treatment.

For CS, the diagnosis of con genital syphilis was based on the criteria established by Kaufmann.6,13 A definite case of congenital infection required identifying T pallidum specimens from lesions by darkfield microscopy or histologic examination. Probable case of congenital syphilis required clinical manifestation of disease, along with a confirmatory microhemagglutinen assay for antibodies to T pallidum, a rising VDRL over the first 3 months of life, or a persistent VDRL over the first 4 months of life.

Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up?

There is not information about time of follow up

 Yes
No
Unclear X
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

No for gestational age time to deliver or re-infected. Authors do not use robust analysis for causal inference

 Yes
No X
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

No

 Yes
No X
Unclear
1.16 Are confidence intervals for the absolute effect of the intervention presented Yes X
No
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes X
No
Unclear
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
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Risk of Bias Assessment

Risk of selection bias “Unclear”

Performance and detection Bias: High (1.10, 1.11 Inadequate treated)

Incomplete data Bias: Unclear

Confusion bias: High

Other problems: Yes

Overall; High Risk

Effect of treatment in cohort studies

1. Congenital syphilis

1.1. Seven studies 12,27,28,31,32,34,35 assessed the use of penicillin in 5,155 foetuses exposed to gestational syphilis during the third trimester. The pooled incidence of congenital syphilis might be 8% (95% CI: 5-11%; I2 = 97.2%). Certainty of evidence: low (very high risk of bias; heterogeneity and upgraded one level due to magnitude of effect) (Figure 3A). Higher heterogeneity was observed in studies mixing in one goup incomplete and not treated women with GS treatment cohorts 31,35 (range: 3-28%; 2,739 patients). Two studies 12,31,35 assessed benzathine penicillin G in 159 foetuses treated within the last four weeks of gestation, with congenital syphilis incidence ranging from 6.5% to 23.4%. However, the actual effect is uncertain due to very low certainty of evidence (very high risk of bias; imprecision) (Table 2).

Figure 3. Incidence of CS and Stillbirths in women with GS treated with penicillin in the third trimester of pregnancy (A. Congenital Syphilis n= 5298; B. Stillbirth n= 2070).

Figure 3

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Source: Authors.

1.2. One cohort 30 evaluated the use of aminopenicillins in 14 foetuses exposed to syphilis eight weeks prior to delivery. The incidence of congenital syphilis could be 42.9% (95% CI: 19-69%). Certainty of evidence: low (high risk of bias; imprecision; and upgrade because substantial magnitude of treatment failure).

1.3. Three studies 28,32,34 reported the incidence of congenital syphilis in 3,262 pregnant women who did not receive any treatment. Incidence ranged from 2% to 12.2%, but the effect remains uncertain due to very low certainty of evidence (very high risk of bias; imprecision) (see Supplementary Appendix 6 Figure S1). One study 27 reported a cohort of 8,795 women with gestational syphilis, which included both untreated women and those who received treatment less than 30 days before delivery; the reported incidence of congenital syphilis was 3.97%.

Appendix 5. Risk of bias of cases series (JBI tool)
In thi Study
Camacho et al36 2021 Sheffield J, et al.37 2002 Yanase et al.38 2025
Were there clear criteria for inclusion in the case series? Yes Unclear Yes
Was the condition measured in a standard, reliable way for all participants included in the case series? Yes Unclear Yes
Were valid methods used for identification of the condition for all participants included in the case series? Yes Yes Yes
Did the case series have consecutive inclusion of participants? Unclear Yes Yes
Did the case series have complete inclusion of participants? Unclear Yes Yes
Was there clear reporting of the demographics of the participants in the study? Yes Yes Yes
Was there clear reporting of clinical information of the participants? Yes Yes Yes
Were the outcomes or follow up results of cases clearly reported? Yes No Yes
Was there clear reporting of the presenting site(s)/ clinic(s) demographic information? Yes Yes No
Was statistical analysis appropriate? Not applicable Not applicable Not applicable
Overall appraisal: Include Include Include
Total (out of 10) 7 6 9
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Figure S1. Heterogeneity assessment: incidence of congenital syphilis in untreated women with gestational syphilis.

Figure S1

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2. Maternal treatment failure

One cohort 12 evaluated treatment failure in 77 women treated with benzathine penicillin G according to syphilis stage. Incidence was 1.3% (95% CI: 0.03-7%), but incidence of failure may be higher or lower because certainty of evidence: very low (high risk of bias; heterogeneity; imprecision). Another study (30) assessed 14 pregnant women treated with amoxicillin or ampicillin for 30-78 days; failure rate was 14.3% (95% CI: 1.8-42.8%). Certainty of evidence: low (high risk of bias; imprecision; upgraded due to frequency of failures).

Secondary Outcomes

3. Stillbirth due to gestational syphilis

3.1. Three studies 32-34 reported on stillbirth in pregnant women treated with penicillin. The pooled incidence was 2% (95% CI: 1-2%; 2,070 patients) (Figure 3B).

3.2. In the study by Nishijima et al. 30, stillbirth occurred in one of 14 women treated with aminopenicillins (7%; 95% CI: 0.2-33.9%) (Table 2).

3.3. Two studies 32,34 reported stillbirths among 2,109 untreated women. Incidence ranged from 1.8% to 3.1%. Nevertheless, the effect of antibiotics in stillbirth is uncertain because certainty of evidence is very low because (very high risk of bias; heterogeneity; imprecision).

4. Prematurity

4.1. Three studies 32-34 reported preterm birth in 2,075 women treated with penicillin. Incidence ranged from 12.2% to 14.6%, with substantial heterogeneity (I2 = 81.83%) (Supplementary Appendix 6 Figure S2).

Figure S2. Heterogeneity assessment: incidence of preterm birth in women with gestational syphilis treated with penicillin.

Figure S2

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4.2. Watson-Jones et al. 33 additionally assessed prematurity using the Dubowitz score in 69 women, reporting a 5.7% incidence (95% CI: 1.6-14.2%) (Table 2).

4.3. Two studies 32,34 reported preterm birth in untreated women; incidence ranged from 10.5% to 14% (2,109 participants) (Table 2).

Though prematurity incidence might be higher or lower because certainty of evidence was qualified very low (very high risk of bias; heterogeneity; imprecision).

5. Safety

5.1. None of the included studies assessed serious adverse events.

5.2. One cohort 30 evaluated non-serious adverse events in 14 women treated with aminopenicillins. Mild adverse events occurred in 21.4% (95% CI: 4.7-50.8%). However, the estimation is uncertain due to very low evidence (very high risk of bias; imprecision) (Table 2).

Effect of treatment in case series

Three case series were included. In one study 37, 43 neonates with confirmed congenital syphilis were reported. Among them, 32 mothers (74%) had received benzathine penicillin G during the third trimester; 28 were treated less than 30 days before delivery. Of these, 68% (19/28) delivered within 10 days of treatment, and 50% of deliveries were preterm.

A second case series 36 described four cases of congenital syphilis with hydrops fetalis. Two women were diagnosed with GS at 26 and 29 weeks of gestation and treated with intravenous aqueous crystalline penicillin G (5 million units every 4 hours for 14 days). Hydrops resolved in both foetuses. At delivery, maternal VDRL titres declined (from 1:64 to 1:2 at 37 weeks and from 1:32 to negative at 36 weeks). Neither neonate had clinical or radiological signs of congenital syphilis; VDRL titres were 1:8 and negative, respectively. Both infants received a prophylactic intramuscular dose of aqueous crystalline penicillin G (50,000 units). No follow-up data at six months were available.

The third case series 38 reported five cases of congenital syphilis with hydrops fetalis. Four were diagnosed at 26 weeks’ gestation, and one beyond 28 weeks. Two women received intravenous aqueous crystalline penicillin G; both neonates responded favorably. Of the three women who received intramuscular benzathine penicillin G, two delivered neonates with congenital syphilis and one neonate responded to treatment. The certainty of evidence was very low (very high risk of bias; imprecision), rendering the actual effect uncertain.

DISCUSSION

This systematic review on the effects of benzathine penicillin G for the treatment of gestational syphilis in the third trimester informs absolute incidence of congenital syphilis might be of 8%. However, substantial heterogeneity was observed, which may in part be explained by the inclusion of studies that combined adequately and inadequately treated cases or complete and incomplete treatment regimens (see Supplementary Material Appendix 6). Furthermore, the use of aminopenicillins appears to be associated with a higher incidence of treatment failure (14%) and a notably elevated incidence of congenital syphilis (43%). The effectiveness of benzathine penicillin G administered four weeks before delivery in preventing congenital syphilis remains uncertain. In addition, safety data on its use during the third trimester are limited.

Amplitude of the search and applicability of the evidence. We conducted a comprehensive search across three major databases and supplemented it with snowballing. A limitation of our approach was the inclusion of only three languages. Our findings support current guideline recommendations regarding the benefit of benzathine penicillin G for managing gestational syphilis and preventing congenital syphilis in the third trimester. The available evidence neither confirms nor refutes the adequacy of benzathine penicillin G when administered within 30 days of delivery.

Comparability of results. We identified three systematic reviews (SRs) evaluating the effects of benzathine penicillin G in gestational syphilis during the third trimester 38-40. Qin et al. 40 conducted a review comparing perinatal outcomes in women with gestational syphilis versus those without syphilis. This SR was rated as low quality (AMSTAR 2: 6/16). In a subgroup analysis of 19 studies involving treatment after 28 weeks’ gestation, the pooled incidence of congenital syphilis was 40.6% (95% CI: 31.3-50.7), notably higher than our estimate. This discrepancy may be explained by the predominance of Chinese studies (17/19), which may differ in diagnostic thresholds and treatment standards. It was also unclear whether cases of possible congenital syphilis were misclassified as confirmed, potentially introducing detection bias. Three studies included in our review 31,33,35 were also included in theirs. Another SR by Pascoal et al. 39 investigated risk factors for congenital syphilis (AMSTAR 2: 7/16). While it included eight cohort studies, it did not report congenital syphilis incidence among infants born to women diagnosed and treated after 28 weeks. One of its included studies overlapped with ours 28.

The use of intravenous aqueous crystalline penicillin G during the third trimester was addressed in a review of case series by Yanase et al. 38, which included the study by Camacho et al. 36. That review reported nine cases of hydrops fetalis in foetuses of mothers treated with intravenous aqueous crystalline penicillin G. Six had a complete response, two partial responses, and one resulted in intrauterine death. Five of the complete responses occurred in foetuses diagnosed at or beyond 28 weeks. In contrast, of nine foetuses treated with intramuscular benzathine penicillin G, only two had complete responses, four partial, and three had no response two of whom died in utero. The authors hypothesised that intravenous aqueous crystalline penicillin G may offer advantages in cases involving systemic infection. Although based on low-certainty evidence from case series, this observation raises a plausible hypothesis: that intravenous penicillin G could be beneficial in treating foetuses infected with T. pallidum late in gestation. Therefore, the safety and efficacy of maternal intravenous aqueous crystalline penicillin G during the third trimester require further evaluation.

Limitations. A potential limitation of this review is selection bias from excluding studies published before 1999. However, studies from earlier decades often lacked clear definitions of “possible syphilis”, a term formally introduced in 2005 4. We did not assess publication bias. Additionally, reporting of safety outcomes across treatment alternatives was limited.

Implications for clinical practice. Until more robust evidence becomes available, pregnant women diagnosed with gestational syphilis before 37 weeks’ gestation should receive at least one intramuscular dose of benzathine penicillin G. If delivery occurs within 30 days of treatment, the neonate should be managed in accordance with current guidelines for “possible congenital syphilis”, including a 10-day course of intravenous aqueous crystalline penicillin G 4,13,14.

Implications for research Although only case series suggest that maternal intravenous aqueous crystalline penicillin G may prevent congenital syphilis in foetuses infected in utero prior to maternal treatment, these findings point to a potential therapeutic window during the final four weeks of pregnancy. This is supported by the following considerations:

  1. Between 2.5% and 27% of neonates with congenital syphilis may have central nervous system (CNS) involvement 41-43.

  2. The only effective treatment for neurosyphilis is aqueous crystalline penicillin G 4, which crosses the inflamed blood-brain barrier more effectively than benzathine penicillin G (44, 45).

  3. This is biologically plausible, given that aqueous crystalline penicillin G crosses the placenta and achieves foetal concentrations equivalent to maternal levels 46.

  4. Current guidelines recommend hospitalization and invasive therapy for neonates with “possible congenital syphilis”, increasing the theoretical risk of healthcare-associated infections 47. This risk could potentially be mitigated by administering intravenous aqueous crystalline penicillin G to the mother for 10 days before delivery, thereby achieving therapeutic foetal levels. Therefore, randomized controlled trials are needed to compare the maternal and neonatal outcomes of intravenous aqueous crystalline penicillin G versus benzathine penicillin G when administered up to eight weeks before delivery

CONCLUSION

Treatment of gestational syphilis with benzathine penicillin G during the third trimester is effective in reducing the risk of congenital syphilis. However, as its efficacy remains uncertain when administered fewer than 30 days before delivery, neonates born within this period should continue to be managed according to current guidelines for possible congenital syphilis. Aminopenicillins appear to be associated with a high rate of treatment failure. Alternative strategies to treat the foetus during the final four weeks of pregnancy are needed to reduce the risk of congenital syphilis.

Ethical issues

The project was approved by the Medical School Ethical Committee at the Universidad National de Colombia. Minute number 001 of 2023

Differences between protocol and review:

  • We changed the inclusion of studies by type of treatment from those that compare antibiotic treatment with any type of penicillin and alternative treatments by inclusion of studies that used any penicillin or other antibiotics (β-lactams or macrolides) with or without a comparison group. Based on the fact we found some cohorts without control group that evaluate the congenital syphilis incidence. We included studies published in Portuguese.

  • We prioritized first perinatal outcomes over maternal outcomes.

  • Cohorts were not evaluated by using the Newcastle - Ottawa tool. The assessment bias for a series of exposure to intervention without a control group was done with a tool included in supplementary material designed by our group.

  • Since current guidelines for the management of gestational and congenital syphilis recommend considering as “infected” all neonates born with less than 4 weeks of treatment, the more important effect measure is the actual cumulative incidence of congenital syphilis in those neonates whom receive any antibiotic treatment, taking into consideration the time between treatment and the delivery. Likewise, this approach allow us to estimate the antibiotic effect in the newborn, in cohorts with or without control group. Therefore, it is more appropriate to use the pooled estimate of incidence or absolute risk of congenital syphilis as the primary outcome measure.

We did not estimate Relative Risk or Odds ratio because this approach is appropriate when the a priori hypothesis assumes no difference between two options, such as comparing treatment versus no treatment. Therefore, in this context, the use of relative risk or risk difference may not be informative.

Supplementary material

TABLE OF CONTENTS

Appendix 1. Protocol

Appendix 2. Search Strategies

Appendix 3. Risk of bias in cohorts studies withuout control group. GETS tool

Appendix 4. List of excluded studies

Appendix 5. Risk of bias assessment of included studies

Appendix 6. Risk of bias of cases series (JBI tool)

Appendix 7. Additional figures

APPENDIX 1. PROTOCOL

1. DESCRIPTION OF THE PRELIMINARY PROJECT:

Formulation of the research problem:

Gestational syphilis is defined as infection by Treponema pallidum acquired during pregnancy or a previously infected woman who becomes pregnant. This condition can affect the foetus due to transplacental transmission of Treponema, which corresponds to what we know as congenital syphilis, this infection increases the risk of abortion, foetal death, preterm birth, low birth weight, neonatal infection, early neonatal death and congenital malformations 1. GS and CS are on the rise in Colombia; the National Institute of Health has reported an increase between 2016 and 2020 of gestational and congenital syphilis, with a prevalence ratio that increased from 6.6 x 1000 live births (LB) to 13.5 x 1000 LB and congenital syphilis from 1.11 to 2.17 x 1000 LB respectively 2. Diagnosis and treatment of GS are the same as in non-pregnant women and me., based on screening with non-treponemal test (NTT) and confirmation with treponemal tests (TT) in the usual diagnostic strategy or with the inverse strategy that is used more in high-risk population or at scenarios of low setting resources. Benzathine penicillin is the election treatment for T pallidum infection and the dose depends on the stage of syphilis 3.

The opportune detection and treatment GS is a relatively simple and cost-effective intervention, even in low-resource settings, in preventing adverse outcomes associated with CS 4. The strategy of early diagnosis with rapid tests and immediate treatment (on the same day) with at least one dose of benzathine penicillin leads to a reduction of about 98% in the incidence of CS (relative risk (RR), 0.02; 95% confidence interval (CI: 0.00-0.18) and a reduction of half the risk of perinatal death (RR, 0.50; 95% CI: 0.33-0.84) (5) as long as treatment for GS been administered 30 days before delivery 5. Other treatment options that have been evaluated, such as doxycycline and tetracyclines, are contraindicated in pregnancy because they are potentially toxic to the foetus (category D) 6. Regarding azithromycin, an antibiotic of the macrolide class, classified as category B in pregnancy, azithromycin has been detected in the umbilical cord and amniotic fluid 6; however, some studies indicate that macrolides do not adequately cross the placental barrier 7,8. Regarding Ceftriaxone, there are no adequate studies to assess its effects in women with gestational syphilis 9. To date, no alternative therapies to penicillin have been described that reliably cross the placenta to treat both the mother and the foetus 10

Penicillins are bactericidal drugs that inhibit the synthesis of the bacterial peptidoglycan cell wall during active multiplication, killing susceptible bacteria 11. To date, penicillin remains effective for managing syphilis, with no evidence of resistance. Crystalline penicillin has been administered over time as a treatment for neurosyphilis, and it is administered by continuous intravenous, intermittent, or intramuscular injection. It is distributed in most tissues and body fluids, including lung, liver, bone, kidney, muscle, sputum, bile, urine and peritoneal, pleural and synovial fluid. It also penetrates the inflamed meninges and reaches therapeutic levels in the CSF, which is helpful in the management of neurosyphilis 12.

Globally, there are a significant number of women who do not attend prenatal care early, who only go to health services for childbirth care, or who, due to deficiencies in access or quality of care services, are not detected promptly with gestational syphilis. Therefore, there is reasonable doubt about what the literature says about the most effective antibiotic treatment regimen (in terms of dose, cycle length and mode of administration) for congenital syphilis in the last 12 weeks before delivery in women diagnosed with gestational syphilis. If the treatment is effective, it will not justify waiting until birth to start treatment, which benefits both the mother and the foetus and the new-born, in addition to reducing the costs for the treatment of the new-born and avoiding sequelae that affect the quality of life of the patient diagnosed with congenital syphilis.

Based on the above, this review will evaluate the evidence that supports different management alternatives, including benzathil penicillin cephalosporins, macrolides, and other types of penicillin, used in the last 12 weeks of pregnancy to treat GS and to prevent or treat CS and its complication

Research question:

What is the safest and most effective antibiotic treatment regimen for congenital syphilis in the last twelve weeks before delivery in women diagnosed with gestational syphilis?

Primary objective

To evaluate the safety and effectiveness of the different treatment alternatives for congenital syphilis with untreated gestational syphilis or with suspected reinfection in the third trimester

Secondary objectives: To determine the safety and effectiveness of the different treatment regimens for gestational syphilis for the prevention of congenital syphilis by gestational age and time

Methodology

Design: Systematic review of interventions

Criteria for considering studies for this review

Types of studies: We plan to include controlled clinical trials and case-control trials in this review.

In case of not finding them, quasi-experimental studies, cohort studies, and case series will be included

Type of population: Participants of interest will be patients with a diagnosis confirmed gestational syphilis with a pregnancy of 28 weeks or more or patients who have suspected reinfection

Type of intervention

We will include studies that compare antibiotic treatment with any type of penicillin and alternative treatments, we will include all administration routes, doses and regimens without limits

Exclusion criteria. Studies where it is not possible to identify a separate way the women who receive treatment for GS in the third trimester

Type of outcome measures. Primary outcomes:

  • Effectiveness: Maternal: Treatment failure for gestational syphilis. Treatment failure for congenital syphilis: evidenced by clinical signs, serological or cerebrospinal fluid titers equal to or greater than 4 times those of the mother and increased postnatal titers.

  • Safety; O Presence of serious and non-serious adverse events related to the drug (systemic allergic reactions), Jarisch-Herxheimer reaction in the mother. O Adverse events in the foetus.

Search Strategies

The following databases will be searched from 1990 to date, obtaining the results according to the term and the Boolean operator used: Cochrane Central Register of Controlled Trials, PUBMED, EMBASE. Other resources: We will check the bibliographies of the included studies and any relevant systematic reviews identified for additional references to relevant studies. We will contact experts and organizations to obtain additional information on relevant studies. If necessary, we will contact the authors of the included studies to clarify the data and obtain more information. There are no limits regarding the time of publication; Languajes only publishes studies in English and Spanish.

Selection of studies

Titles and abstracts obtained by electronic search will be downloaded from a reference management database, and duplicates will be removed. Two reviewers (VM AG) will independently screen titles and abstracts for inclusion. We will retrieve full-text reports and publications, then independently screen the complete text, identify studies for inclusion and identify and record reasons for exclusion of ineligible studies. We will resolve any disagreements by discussion or, if necessary, consult a third review author (HG). We will list studies that initially appeared to meet the inclusion criteria but were later excluded in the characteristics of excluded studies table.

Data extraction and management

We will use a standard data collection form to study the characteristics and outcome data. Two reviewers (VM and AG) will independently extract characteristics of the included studies that include Methods: study design, number of study centres and location, study setting, withdrawals, study date, follow-up, and method of adjustment for design effects or confounding. Participants: number, mean age, parity, inclusion criteria, exclusion criteria, and other relevant characteristics. Intervention: dose, route, regimen, co-interventions, comparison and efficacy and safety primary or secondary outcomes.

Two reviewers (VM, AG) will independently extract outcome data from included studies. If outcome data were reported unusable, this would be indicated in the characteristics of the included studies table. Disagreements will be resolved by consensus or by involving a third reviewer (HG).

Risk of bias assessment in included studies

Two reviewers (VM, AG) will independently assess the risk of bias for key outcomes defined in this protocol using the Rob 2 tool for randomised studies and Robins for non-randomised studies. We will use the Newcastle Ottawa tool for cohort studies and the JBI Evidence Synthesis critical appraisal tool for case series. We will resolve disagreements by discussing or involving another author (HG).

Treatment effect measures

Data synthesis: This will be done narratively regarding the type of design, population, type of population included, intervention and risk of bias according to the kind of design. Unit of analysis: live births, stillbirths Effect measures: relative risk (RR) or odds ratio (OR) difference in cumulative incidence (risk difference)

Subgroup analysis: Subgroup analysis will be done according to gestational age of treatment between 28 and 31 6/7 weeks 32 to 35 6/7 and 36 or more weeks. The number of doses administered to the mother of the study drug and the diagnosed foetal compromise evidenced by ultrasound will also be analysed. A population subgroup will be analysed, including 4, 8 and 12 weeks before delivery.

Presentation of results: It will be done descriptively by type of design. The possibility of making a pooled estimate of the effect will be evaluated if the mixture of treatments or populations makes sense and depending on the heterogeneity of the results by type of design.

Ethical Considerations

This is a systematic review study without any intervention. The study will consider the ethical considerations of Resolution No. 8430 of 1993 of the Ministry of Health, which establishes the scientific, technical and administrative standards for research on humans. Article 11 of this resolution establishes the risks of research on humans, and according to this classification, this project is classified as "Research without risk", which includes retrospective documentary research techniques and methods and those in which no intentional intervention or modification of the biological, physiological, psychological or social variables of the individuals participating in the study is carried out. The results obtained at the end of the study will be used solely for scientific purposes

BIBLIOGRAPHY

1. Gomez GB, Kamb ML, Newman LM, Mark J, Broutet N, Hawkes SJ. Untreated maternal syphilis and adverse outcomes of pregnancy: a systematic review and meta analysis. Bull World Health Organ. 1 de marzo de 2013;91(3):217-26.

2. Ministerio de salud. Colombia ETMI-Plus. Estrategia nacional para la Eliminación de la Transmisión Maternoinfantil de la Infección por el VIH, la Sífilis, Hepatitis B y la a enfermedad de Chagas, Colombia 2019 - 2030 Alerta No 1 Comportamiento de la sífilis Gestacional y congénita.

3. Ortiz DA, Shukla MR, Loeffelholz MJ. The Traditional or Reverse Algorithm for Diagnosis of Syphilis: Pros and Cons. Clin Infect Dis. 2020;71:S43-S51. doi: 10.1093/cid/ciaa307.

4. Kuznik A, Muhumuza C, Komakech H, Marques EMR, Lamorde M. Antenatal Syphilis Screening Using Point- Of-Care Testing in Low- and Middle-Income Countries in Asia and Latin America: A Cost-Effectiveness Analysis. Rubens C, editor. PLOS ONE. 26 de mayo de 2015;10(5):e0127379.

5. World Health Organisation. The global elimination of congenital syphilis: rationale and strategy for action. WHO. 2007. Disponible en: http://www.who.int/reproductivehealth/publications/rtis/9789241595858/en/.

6. Boelig RC, Lam E, Rochani A, Kaushal G, Roman A, Kraft WK. Longitudinal evaluation of azithromycin and cytokine concentrations in amniotic fluid following one time oral dosing in pregnancy. Clin Transl Sci. noviembre de 2021;14(6):2431-9.

7. Heikkinen T, Laine K, Neuvonen PJ, et al. The transplacental transfer of the macrolide antibiotics erythromycin, roxithromycin and azithromycin. BJOG 2000;107(6):770-5

8. Ramsey PS, Vaules MB, Vasdev GM, et al. Maternal and transplacental pharmacokinetics of azithromycin. Am J Obster Gynecol 2003;188(3):714-18

9. WHO Guidelines for the Treatment of Treponema pallidum (Syphilis). Geneva: World Health Organization; 2016. PMID: 27631046.

10. Workowski KA, Bachmann LH. Centers for Disease Control and Prevention’s Sexually Transmitted Diseases Infection Guidelines. Clin Infect Dis. 13 de abril de 2022;74(Supplement_2):S89-94.

11. Wise EM, Park JT. Penicillin: its basic site of action as an inhibitor of a peptide cross-linking reaction in cell wall mucopeptide synthesis. Proc Natl Acad Sci U S A. 1965 Jul;54(1):75-81

12. Peeling RW, Mabey D, Kamb ML, Chen XS, Radolf JD, Benzaken AS. Syphilis. Nat Rev Dis Primer. 12 de octubre de 2017;3:17073.

APPENDIX 2. SEARCH STRATEGIES

Search electronic report #2
Database EMBASE
Platform Embase.com
Search Date 30/Jun/2025
Range of search date None
Language restrictions None
Other limits None
Search strategy (results)
  1. 'syphilis'/exp (52862)
  2. 'latent syphilis'/exp (529)
  3. 'congenital syphilis'/exp (4550)
  4. 'syphilis serology'/exp (7193)
  5. 'treponema pallidum'/exp (8927)
  6. syphilis:ti,ab (37531)
  7. lues:ti,ab (786)
  8. (treponema NEAR/1 pallidum):ti,ab (6666)
  9. (great NEAR/1 pox):ti,ab (12)
  10. (hutchinson* NEAR/1 teeth):ti,ab (4)
  11. #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 (62516)
  12. 'pregnancy'/exp (962156)
  13. 'pregnant person'/exp (139955)
  14. pregnan*:ti,ab (903877)
  15. gestat*:ti,ab (392598)
  16. gravid*:ti,ab (25148)
  17. #12 OR #13 OR #14 OR #15 OR #16 (1430225)
  18. #11 AND #17 (6174)
  19. 'penicillin derivative'/exp (415095)
  20. 20 'penicillin g'/exp (87283)
  21. 'benzathine'/exp (267)
  22. 'procaine penicillin'/exp (5330)
  23. penicil?in*:ti,ab (78593)
  24. benzylpenicillin*:ti,ab (3235)
  25. benzathine:ti,ab (1976)
  26. 'ampicillin'/exp (113496)
  27. ampicillin:ti,ab (37467)
  28. 'cephalosporin derivative'/exp (316740)
  29. cephalospor*:ti,ab (39504)
  30. 'cefotaxime'/exp (54722)
  31. cephotaxim*:ti,ab (110)
  32. cefotaxim*:ti,ab (14475)
  33. 'ceftriaxone'/exp (91391)
  34. ceftriaxon*:ti,ab (26407)
  35. 'macrolide'/exp (469232)
  36. macrolide*:ti,ab (27461)
  37. 'erythromycin'/exp (91419)
  38. erythromycin*:ti,ab (30113)
  39. 'azithromycin'/exp (60641)
  40. azithromycin*:ti,ab (21759)
  41. 'clarithromycin'/exp (46584)
  42. clarithromycin:ti,ab (17648)
  43. 'probenecid'/exp (11513)
  44. probenecid:ti,ab (5176)
  45. #19 OR #20 OR #21 OR #22 OR #23 OR #24 OR #25 OR #26 OR #27 OR #28 OR #29 OR #30 OR #31 OR #32 OR #33 OR #34 OR #35 OR #36 OR #37 OR #38 OR #39 OR #40 OR #41 OR #42 OR #43 OR #44 960358
  46. #18 AND #45 1397
  47. #18 AND #45 AND ([embase]/lim OR [preprint]/lim) (1121)
# of records identified 1121
# of records without duplicates 1110
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Search electronic report #3
Database EBM Reviews - Cochrane Central Register of Controlled Trials
Platform Ovid
Search Date 30/Jun/2025
Range of search date None
Language restrictions None
Other limits None
Search strategy (results)
  1. exp Syphilis/ (215)
  2. exp Syphilis, Latent/ (5)
  3. exp Syphilis, Congenital/ (13)
  4. exp Syphilis Serodiagnosis/ (29)
  5. exp Treponema pallidum/ (29)
  6. syphilis.tw (832)
  7. lues.tw (6)
  8. (treponema adj1 pallidum).tw. (89)
  9. (great adj1 pox).tw (0)
  10. (hutchinson$ adj1 teeth).tw (0)
  11. or/1-10 (915)
  12. exp Pregnancy/ (32926)
  13. exp Pregnant People/ (0)
  14. pregnan$.tw (75758)
  15. gestat$.tw (31937)
  16. gravid$.tw (1243)
  17. or/12-16 (101087)
  18. 11 and 17 (194)
  19. exp Penicillins/ (6704)
  20. exp Penicillin G/ (5509)
  21. exp Penicillin G Benzathine/ (140)
  22. penicil?in$.tw (2591)
  23. benzylpenicillin$.tw. (117)
  24. benzathine.tw (183)
  25. ampicillin.tw (1556)
  26. exp Cephalosporins/ (5156)
  27. cephalospor$.tw. (1542)
  28. exp Cefotaxime/ (1652)
  29. cephotaxim$.tw (2)
  30. cefotaxim$.tw (786)
  31. exp Ceftriaxone/ (855)
  32. ceftriaxon*.tw. (1706)
  33. exp Macrolides/ (11914)
  34. macrolide$.tw (1210)
  35. exp Erythromycin/ (4282)
  36. erythromycin$.tw (1863)
  37. exp Azithromycin/ (1525)
  38. azithromycin$.tw (3355)
  39. exp Clarithromycin/ (1741)
  40. clarithromycin.tw (3431)
  41. exp Probenecid/ (314)
  42. probenecid.tw (489)
  43. or/19-42 (29078)

1 44 18 and 43 (38)
# of records identified 38
# of records without duplicates 19
Open in a new tab

APPENDIX 3. RISK OF BIAS IN COHORT STUDIES WITHOUT CONTROL GROUP. GETS TOOL

Risk of Bias Assessment

Selection Bias Selection Bias (Item 1.2 -1.5)

  • Low: All of items 1.2 to 1.5 are responded Yes

  • Moderate: Item 1.3 is responded No

  • High: Items 1.2, 1.4, or 1.5 are responded No

  • Unclear: Two or more items are unclear

Performance and Detection Bias (Item 1.6 - 1.12)

  • Low: All of items 1.6 to 1.12 are responded Yes

  • Moderate: One item responded No

  • High: Two or more items are responded No

  • Unclear: Two or more items are unclear

Attrition Bias (Item 1.13)

  • Low: Item 1.13 is responded Yes

  • High: The item is responded No

  • Unclear: The item is unclear

Confounding Bias (Item 1.14)

  • Moderate: Robust methodologies (e.g., causal inference: time series, segmented regression, before and after study assuming no independence, etc.) are used to control confounding factors

  • High: Descriptive post-intervention measures or pre-post comparisons assuming independence are used

Other Issues (Items 1.15-1.16)

  • Low: Both items are responded Yes

  • Moderate: One item is responded No

  • High: Both items are Responded No

  • Unclear: Both items are unclear

Overall Risk of Bias

  • Low Risk: All domains have low risk of bias and no other relevant issues

  • High Risk: One domain has high risk of bias and no other issues

  • Very High Risk: Two or more domains have high risk of bias, or one domain with high risk and additional relevant issues

APPENDIX 4. LIST OF EXCLUDED REFERENCES

APPENDIX 5. RISK OF BIAS ASSESSMENT OF INCLUDED STUDIES

Checklist for series of subjects exposed to intervention studies
Reference: Dou L, Wang X, Wang F, Wang Q, Qiao Y, Su M, Jin X, Qiu J, Song L, Wang A. Epidemic Profile of Maternal Syphilis in China in 2013. Biomed Res Int. 2016;2016:9194805. doi: 10.1155/2016/9194805.
Checklist verified by: HGD, AMGT
Section 1 Internal Validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) This study is. (Mark with an X the selected answer)
1.1 Does the study define an appropriate, clear, and focused research question? to describe the epidemiological characteristics of pregnant women with maternal syphilis and their pregnancy outcomes in China in 2013 Yes
No
Unclear X
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

Pregnant women who met the following criteria and their children were included in the analysis: (1) syphilis screening tests positive during pregnancy and delivery at health facilities;

(2) being diagnosed with syphilis; (3) being registered in the surveillance system; (4) delivered at gestational age of 28 weeks or more in 2013

 Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

Newborns with congenital syphilis born to women who received no syphilis tests were excluded from the analyses

 Yes X
No
Unclear
1.4

What proportion of eligible subjects participated in the study?

In 2013, a total of 15884 pregnant women with laboratory-confirmed syphilis infection delivered and were registered in Information System of Prevention of Mother to child transmission of syphilis management in China. All of them were considered to the analysis

 Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

It looks like yes

 Yes X
No
Unclear
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Tables 1, 2, 3

Yes X
No
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

For those with positive syphilis tests appropriate treatment will be initiated promptly with at least 2 courses of penicillin treatment, one at early pregnancy stage and one at the third trimester. For each course women will receive either benzathine or procaine penicillin treatment by intramuscular injection, as recommended by the guide lines.

Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Inadequate treatment for maternal syphilis was defined as nontreatment or nonpenicillin treatment, less than 2 completed courses of treatment during pregnancy, or less than 2 weeks between the 2 courses of treatment

In the group of women with treatment in the last 4 weeks, it is not possible to identify who was treated and who was not treated or who was inadequately treated, so there is detection bias when mixing them.

Yes
No X
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is not information

 Yes
No
Unclear X
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open label study Hard outcomes

 Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

Gestational age is not defined

Time between treatment and delivery was not considered

 Yes
No
Unclear X
1.12

Are outcome variables adequately defined and measured?

Congenital syphilis in new-born was defined as having at least one of the following situations in infant who was younger than 6 weeks and born to syphilis infected mother: (1) positive treponemal test and high titer of nontreponemal test (a value 4-fold higher than that of his/her mother’s before delivery); (2) laboratory confirmation of Treponema pallidum in clinical specimens by dark-field microscopy; or (3) reactive treponemal antibody test of IgM.

“Any adverse pregnancy outcomes” are a composite outcome in our analysis, which include preterm delivery, LBW, stillbirth, neonatal death, and congenital syphilis in newborns.

Preterm delivery was defined as a delivery that occurs before

37 gestational weeks. Low birth weight (LBW) was defined as birth weight of a live-born baby of less than 2,500g at birth. Stillbirth was defined as death of a foetus of at least 28 gestational weeks. Neonatal death was defined as death of live-born baby who died during the first week after birth.

Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up?

Apparently, there was not

 Yes
No X
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

Authors do not describe loss of follow up

 Yes
NO X
Unclear
1.15 Is there an estimation of the required sample size to determine the benefit of the intervention? Yes
NO X
Unclear
1.16 Are confidence intervals for the absolute effect of the intervention presented Yes X
NO
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes X
NO
Unclear
2,2

Are the results of the study directly applicable to the target population of the systematic review?

Not for pregnancy of 37 weeks or more

 Yes
NO
Unclear X
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Risk of Bias Assessment

Risk of selection bias; low

Performance and detection Bias: High (1.8 Inadequate treated)

Incomplete data Bias: Unclear

Confusion bias: High

Other problems: Yes (no CI 95%)

Overall; Very High Risk

Checklist for series of subjects exposed to intervention studies
Reference: Hong FC, Risk of Congenital Syphilis (CS) Following Treatment of Maternal Syphilis: Results of a CS Control Program in China. Clin Infect Dis. 2017 Aug 15;65(4):588-594. doi: 10.1093/cid/cix371
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

To evaluate the efficacy of the CDC recommendations for the treatment of syphilis in pregnancy for the eradication of maternal infection and prevention of congenital syphilis

 Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

Cohorts of pregnant women were structured by data drawn from master datasets to include pregnant women who were identified with syphilis-seroposivity at their first antenatal visit and had information on their treatment status for syphilis. with no treatment before pregnancy

The pregnant women finally included for analyses were limited to those women whose infants had a definite outcome of confirming or excluding a diagnosis of congenital syphilis by October 2016

 Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

There is not information

 Yes
No
Unclear X
1.4

What proportion of eligible subjects participated in the study?

7,498 had Syphilis

6,559 were included (88%)

4,746 were analysed (76%% of those included)

Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

It looks like

 Yes
No
Unclear X
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Tables 1, 3

Yes X
No
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

Intramuscular benzathine penicillin G (BPG) was applied as the first choice to all syphilis-seropositive pregnant women regardless of the disease stage tor at least one course (2.4 million units of BPG once weekly for three consecutive weeks). A second-course of treatment during late pregnancy was applied in the study area before it was recommended by the national PTNCT guidelines in 2012. Procaine penicillin G (PPG) 0.8 million units intramuscularly once daily for 15 days was introduced during 2O03-2008.

Pregnant women who were allergic to penicillin were treated with erythromycin 500 mg orally four times a day for 15 days, azithromycin 500mg orally once a day for 10 days, or ceftriaxone sodium 1 g injection per day for 10 days

 Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Based on treatment status prior to the current pregnancy, the syphilis-seropositive pregnant women were categorized into Group 1 with adequate treatment before pregnancy and Group 2 with no treatment before pregnancy. Each of the groups was further grouped into (1) treatment with early BPG (initiation of BPG or PPG before 28 weeks of gestation), (2) treatment with late BPG (initiation of BPG or PPG at 28 weeks of gestation or later), (3) treatment with other antibiotics and (4) no treatment during pregnancy

 Yes
No
Unclear
1.9 Were any co-interventions applied differentially to the exposed subjects? There is not information Yes
No X
Unclear
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open label study

Hard outcome for CS

 Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

Gestational age

No time between Treatment and delivery

 Yes
No
Unclear X
1.12

Are outcome variables adequately defined and measured?

CS Diagnosis of 4 congenital syphilis (probable or confirmed case) was based on meeting one of the following laboratory criteria: (1) a reactive 19S-IgM?TPPA; (2/ a serum quantitative TRUST titer that was four-fold higher than the mother’s titer; (3) a four-fold or greater rise in TRUST titer during the follow-up; or (4) a reactive TPPA that did not revert to nonreactive by end of 18 months’ follow-up. Stillbirth potentially due to syphilis was not accounted into cases of congenital syphilis.

GS: 3 months to monitor any changes in TRUST titer and TPPA positivity.

Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up? Excluding 889 (11.9%) women who were lost to follow-up

Of these infants, 27.9% were lost from the cohort mainly because of migration of their parents (66.9%)

 Yes X
No
Unclear
1.14 Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)? Properly treated
Unproperly treated X
Not clear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

No, they include all participants

 Yes
No X
Unclear
1.16 Are confidence intervals for the absolute effect of the intervention presented CI 95 it is presented Yes X
No
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes X
No
Unclear
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
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Risk of Bias Assessment

Risk of selection bias “High”

Performance and detection Bias: Low (1.10, 1.11 Inadequate treated)

Incomplete data Bias: High

Confusion bias: High

Other problems: Yes

Overall; Very High Risk

Checklist for series of subjects exposed to intervention studies
Reference: Luengmettakul J, Apiwantana S, Jitrungruengnij N. Incidence of Congenital Syphilis and Adverse Pregnancy Outcomes among Syphilitic Pregnant Women According to the Treatment Adequacy in Tertiary Care Hospital, Thailand. J Med Assoc Thai 2025;108:9-16. DOI: 10.35755/jmedassocthai.2025.1.9-16-01174
Checklist verified by: HGD, AMGT
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

“Study the association of congenital syphilis and adverse pregnancy outcomes between mothers who received adequate treatment and those who received inadequate treatment”.

Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

“The authors consecutively collected the medical records of pregnant women diagnosed with syphilis during pregnancy, provided there were no missing important data, until the specified number was reached”

Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

No information

 Yes
No
Unclear X
1.4

What proportion of eligible subjects participated in the study?

106 of 162 with adequate treatment. 90 with inadequate treatment and 16 without treatment.

65%of adequate treatment

100 % of inadequate treatment + 100% untreated

 Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

Authors don t say how they selected the 106 with adequate treatment.

Yes
No
Unclear X
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

See at Table 1

Yes
No
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

‘Adequate treatment for syphilis infection during pregnancy means receiving a complete course of Penicillin injection at least 30 days before delivery.

Inadequate treatment is defined as receiving a Complete course of penicillin but less than 30 days before delivery, or receiving an incomplete injection, or not receiving an incomplete injection, or not receiving treatment during pregnancy. Mixed inadequately treated with untreated”

Yes
No X
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components, mode of administration)?

“The authors treat early syphilis with benzathine penicillin intramuscularly (IM) for one or two doses. The late syphilis was treated with benzathine penicillin IM weekly for three doses Pregnant women allergic to penicillin might use penicillin sensitization or alternative medications, depending on the patient’s preference”.

Yes X
No
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is not information

 Yes
No X
Unclear
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

The inadequate treatment and not treatment are included in the same group it could carry on to overestimation of CS incidence. In 30% of patients with adequate treatment we do not have data

 Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

There is not information

 Yes
No
Unclear X
1.12

Are outcome variables adequately defined and measured?

“Congenital syphilis is defined by the Centres for Disease Control and Prevention (CDC)(15) as 1) a neonate or foetus with an abnormal physical examination that was consistent with congenital syphilis, 2) a serum nontreponemal serologic titer that was fourfold higher than the mother’s titer, or 3) a pathological placenta confirmed for syphilis infection.

Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up?

Apparently they had no losses

 Properly treated
Unproperly clear
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

Authors do not take into account the time from treatment to delivery or gestational age. No robust statistical methods are used to control for confounding factors.

Yes
No X
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

No, they don't

 Yes
No X
Unclear
1.16

Are confidence intervals for the absolute effect of the intervention presented

Yes

 Yes X
No
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and vour evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes
No
Unclear X
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Risk of Bias Assessment

Risk of selection bias “High”

Performance and detection Bias: High

Incomplete data Bias: Low

Confusion bias: High

Other problems: Yes

Overall; Very High Risk

Checklist for series of subjects exposed to intervention studies
Reference: Nishijima Effectiveness and Tolerability of Oral Amoxicillin in Pregnant Women with Active Syphilis, Japan, 2010-2018. Emerg Infect Dis. 2020 Jun;26(6):1192-1200. doi: 10.3201/ eid2606.191300
Checklist verified by: HGD, AMGT
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

To evaluate the efficacy of the CDC recommendations for the treatment of syphilis in pregnancy for the eradication of maternal infection and prevention of congenital syphilis

 Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

We included pregnant women with syphilis, re gardless of their symptoms, who were treated with oral amoxicillin or ampicillin during 2010-2018; we only included those with serum rapid plasma reagin (RPR) titers >8 and positive results from treponemal tests, such as the T. pallidum hemagglutination test (10,15)

Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

We excluded patients with tertiary syphilis or neurosyphilis diagnoses that were based on findings from cerebrospinal fluid (CSF) samples (10,16) for patient symptoms (including ocular or auditory syphilis) and those with suspected reinfections after initiation of syphilis treatment (defined as patients with >4-fold rise in RPR titer after 4-fold decrement with or without symptoms) (10,15,17).

Yes X
No
Unclear
1.4

What proportion of eligible subjects participated in the study?

80 of 136 (60%) were admitted (Authors do not give reasons for exclusion

 Yes
No
Unclear X
1.5

Were exposed subjects included in strict sequential order?

There is not information

 Yes
No
Unclear X
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Table 1

Properly treated X
Unproperly treated
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

These guidelines recommend oral amoxicillin or ampicillin with dosing of 1,500 mg/day (i.e', 500 mg 3X/d) for 2-4 weeks for primary syphilis, 4-8 weeks for second ary syphilis, and 8-12 weeks for tertiary or later-stage syphilis in pregnant women.

Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Yes

 Yes X
No
Unclear
1.9 Were any co-interventions applied differentially to the exposed subjects? There is not information Yes
No
Unclear X
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open-label study. Hard outcome. Measured with non-treponemal test titers for the mother and serologic examination, and a complete five-titer test for the new-born (probable) and isolation of confirmed tp.

Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

Table 1

Yes X
No
Unclear
1.12

Are outcome variables adequately defined and measured?

The primary outcome of this study was effectiveness of prevention of MTCT of syphilis. We defined MTCT as a CS case and defined CS cases as live newborns with CS diagnoses, miscarriages, or still births. If a live new-born was not given a CS diagnosis, we interpreted the treatment given as successful for preventing M1C1 (5). We evaluated the secondary outcome serologic effectiveness of treatment in the mother (4-fold decrement of serum RPR titer) at each of the following time points: delivery (25), 6 months after therapy (4), and 12 months after. Not in the least 4 weeks

 Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up?

Of the 80 cases, we excluded 9 (6 with unknown outcomes, 3 involving abortions induced at 15-17weeks of pregnancy) from the outcome analysis.

Yes X
No
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

Not reinfection; it appears to have been assumed to be treatment failure. They did not use robust methods to evaluate causal inference.

Yes
No X
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

No

 Yes
No X
Unclear
1.16 Are confidence intervals for the absolute effect of the intervention presented CI are presented Yes X
No
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and vour evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes X
No
Unclear
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Risk of Bias Assessment

Risk of selection bias “High” (1.4) Performance and detection Bias: “Low

Incomplete data Bias: “Low

Confusion bias: “High”

Other problems: Yes

Overall; Very High Risk

Checklist for series of subjects exposed to intervention studies
Reference: Qin JB, Feng TJ, Yang TB, Hong FC, Lan LN, Zhang CL. Maternal and paternal factors associated with congenital syphilis in Shenzhen, China: a prospective cohort study. Eur J Clin Microbiol Infect Dis. 2014 Feb;33(2):221-32. doi: 10.1007/s10096-013-1948-z.
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

The study aimed to investigate the maternal and paternal risk factors for CS.

Properly treated X
Unproperly treated
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

The inclusion criteria were women who: (a) had positive

TRUST and TPPA tests during pregnancy or up to a week after delivery; (b) provided informed consent to be included in the evaluation; (c) continued their pregnancy after treatment; (d) participated in the follow-up process and had a complete case report form (CRF); (e) had a pregnancy outcome that could be clearly evaluated; (f) were not allergic to benzathine penicillin G; and (g) had a negative HIV test

 Properly treated X
Unproperly treated
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

HIV( + ) spontaneous abortion or IVE, ectopic pregnancy, foetal death, allergy to penicillin. Incomplete data

 Properly treated
Unproperly treated X
Unclear
1.4

What proportion of eligible subjects participated in the study?

52%

 Properly treated
Unproperly treated X
Unclear
1.5

Were exposed subjects included in strict sequential order?

There is no information

 Properly treated
Unproperly treated
Unclear X
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Table 1, 3 ,4

Properly treated
Unproperly treated
Unclear X
1.7

Is the intervention applied to the subjects clearly defined?

Gravidas with untreated syphilis were given three injections of 2.4 million units of benzathine penicillin at weekly intervals. At least one dose was given if there was too little time to give injections before delivery

 Properly treated X
Unproperly treated
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Complete syphilis treatment was defined as three doses of benzathine penicillin at weekly intervals [21]. Incomplete treatment was defined as two doses or less of penicillin received.

This data was not taken into account to evaluate the Incidence of CS at GA > 29 week or four weeks before pregnancy

 Properly treated
Unproperly treated X
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is no information

 Properly treated
Unproperly treated
Unclear X
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Hard Outcome see 1.12

 Properly treated X
Unproperly treated
Unclear
1.11

Are prognostic variables adequately defined and measured?

No time to delivery

 Properly treated X
Unproperly treated
Unclear
1.12

Are outcome variables adequately defined and measured?

Diagnosis of congenital syphilis A CS diagnosis required one of the following criteria: (1) a positive dark field or fluorescent antibody test of body fluid; (2) an abnormal physical examination that was consistent with secondary syphilis and a TRUST titer that was four-fold higher than the mother’s titer;(3) a positive o fluorescent trep onemal antibody absorption test with a fluorochrome-labelled antihuman IgM on fractionated sera (FTA- ABS19SIgMtest); or (4) a reactive TPPA test until 18 months after birth [16, 22

 Properly treated X
Unproperly treated
Unclear
1.13

What proportion of subjects were lost to follow-up?

Losses in the follow-up 32% In newborns, there was no measure of the effect in breasts

 Properly treated
Unproperly treated X
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

Authors did not use causal inference for analys

 Properly treated
Unproperly treated X
Unclear
1.15 Is there an estimation of the required sample size to determine the benefit of the intervention? Properly treated
Unproperly treated
Unclear X
1.16 Are confidence intervals for the absolute effect of the intervention presented Properly treated
Unproperly treated X
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes
No
Unclear X
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Risk of Bias Assessment

Selection Bias: high

Performance and detection bias:

Attrition Bias

Confusion Bias

Other problems

Overall Risk

Checklist for series of subjects exposed to intervention studies
Reference: Wan Z, Zhang H, Xu H, Hu Y, Tan C, Tao Y. Maternal syphilis treatment and pregnancy outcomes: a retrospective study in Jiangxi Province, China. BMC Pregnancy Childbirth. 2020 Oct 27;20(1):648. doi: 10.1186/s12884-020-03314-y
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

The purpose of this study was to investigate the impact of maternal treatment during pregnancy-on- pregnancy outcomes in Jiangxi province.

Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

Given that data which included only syphilis infected pregnant women who delivered at gestational age of 28weeks or more (including live births, stillbirth >28 gestational weeks and 0-7days for neonatal deaths) and were registered in Information System of PMTCT of Syphilis Management between 1 January 2013 and 31 December 2019 were enrolled

 Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

61 women were excluded from the study because of delivering multiple pregnancy (46) or lacking of treatment information

 Yes
No
Unclear X
1.4

What proportion of eligible subjects participated in the study?

During 1 January 2013-31 December 2019, 3,945,102 pregnant women were screened for syphilis and” 4271 who delivered at gestational age of 28weeks or more and were registered in Information System of PMTCT of Syphilis Management of Jiangxi Province were enrolled. Among these women, 61 women (1.6%) were excluded from the study because of delivering multiple pregnancy (46) or lacking of treatment information (15), thus resulting in 4210 women included in the final analyses (Fig. 1).

Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

It looks like

 Yes X
No
Unclear
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Table 1

Yes X
No
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

Author do not define clearly the intervention

 Yes
No
Unclear X
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Definitions

Adequate treatment was defined as two completed courses of penicillin treatment with more than 2 weeks (appropriately 4 weeks) between the two courses, and treatment must have been provided at least 28 days prior to delivery or 4weeks gestation. Non-penicillin treatment or treatment with fewer than two completed courses was defined as treated inadequately.

Yes X
No
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is not information

 Yes
No
Unclear X
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

There is not information

 Yes
No
Unclear X
1.11

Are prognostic variables adequately defined and measured?

No data is provided on time between treatment and delivery cases of reinfection. Table 1 does provide information on the trimester of pregnancy at the start of CPN.

Yes X
No
Unclear
1.12

Are outcome variables adequately defined and measured?

Congenital syphilis in new-born was defined as having at least one of the following situations in infant who was younger than 6 weeks and born to syphilis infected mother: (1) positive treponemal test and high titer of nontreponemal test (a value 4-fold higher than that of his/her mother s before delivery); (2) laboratory confirmation of Treponema pallidum in clinical specimens by dark-field microscopy.

It does not describe separately how many patients in the third trimester received adequate or inadequate treatment

 Yes
No
Unclear X
1.13

What proportion of subjects were lost to follow-up?

Lost to follow-up: apparently none The follow-up time for newborns is unclear.

Yes X
No
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

It is not necessary

 Yes X
No
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

No, they include all participants with syphilis

 Yes
No X
Unclear
1.16

Are confidence intervals for the absolute effect of the intervention presented

CI 95 it is presented

 Yes X
No
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes
No
Unclear X
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Risk of Bias Assessment

Selection bias: Low

Performance and detection bias: High(1.8, 1.12)

Attrition bias : Low

Confounding: High

Other problems : CI 95% is not calculated

Overall risk. Very high

Checklist for series of subjects exposed to intervention studies
Reference: Watson-Jones D, Syphilis in pregnancy in Tanzania. II. The effectiveness of antenatal syphilis screening and single-dose benzathine penicillin treatment for the prevention of adverse pregnancy outcomes. J Infect Dis. 2002 ;186(7):948-57. doi: 10.1086/342951
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

We examined whether single-dose benzathine penicillin treatment is adequate to prevent adverse pregnancy outcomes in the Mwanza region of north western Tanzania, where syphilis screening is now being implemented using the single-dose benzathine penicillin regimen and where most pregnant women attend ANCs after 20 weeks of gestation

 Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

From September 1997 through November 1999, all eligible RPR-positive women screened and treated with single-dose benzathine penicillin, followed by the next 2 eligible RPR-negative women attending the ANC, were recruited. Inclusion criteria included informed consent, residence in Mwanza Municipality for at least 1 month, and ultrasound- proven viable pregnancy.

Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

Women with a multiple gestation (i.e., 11 foetus), penicillin allergy, medical complications of pregnancy (hypertension, diabetes, or prior vaginal bleeding), or congenital foetal abnormal

 Yes X
No
Unclear
1.4

What proportion of eligible subjects participated in the study?

1361 Women with RPR ( + ) were candidates. 805 RPR ( + ) were not included were not eligible, predominantly because they were not residents of Mwanza or were planning to leave prior to delivery (55%) Then 556 RPR (+) were included (45%).154 were excluded Were analysed 402 = 153 (high titre) + 249 (low titre) (30%)

 Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

There is no information

 Yes
No X
Unclear
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Table 1

Yes X
No
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

Women who were seronegative for syphilis at the initial ANC screening who were later found to be RPR positive after retesting of serum samples at the reference laboratory were treated for syphilis with benzathine penicillin G (2.4 MUim).

Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

There is no informed

 Yes
No
Unclear X
1.9

Were any co-interventions applied differentially to the exposed subjects?

Recommended treatments at that time included metronidazole for the treatment of T. vaginalis and bacterial vaginosis, cotrimoxazole for the treatment of gonorrhoea and genital ulceration, erythromycin for the treatment of Chlamydia trachomatis, and clotrimazole pessaries for the treatment of vaginal candidiasis if those were tested as ( + )

Yes X
No
Unclear
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open label study

 Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

No time between Treatment and delivery nor reinfection

 Yes
No
Unclear X
1.12

Are outcome variables adequately defined and measured?

The infant was examined and weighed. Stillbirth was defined as a foetal death at 122 weeks of gestation, and intrauterine foetal death (IUFD) was defined as foetal death at 22 weeks of gestation. LBW was defined as birth weight of !2500 grams, preterm birth was defined as delivery at !37 weeks of gestation, and intra uterine growth retardation (IUGR) was defined as LBW after 37 weeks of gestation [21-23]. Gestational age at birth was estimated by 2 methods, ultrasound/LMP dating or a standard Dubovitz ex amination [24] performed on live-born infants within 5 days of birth

 Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up?

42/462 = 12% (Women lost to follow-up before delivery were younger than those followed up (mean age, 22.7 vs. 23.8 years; Pp.01 (41.3% vs. 28.3%) and were more likely to beprimigravidae Pp.03 ) and single (24.7% vs. 34.2%; p< 0.05)

Yes X
No
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

Authors did not perform causal inference analysis

 Yes
No X
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

No

 Yes
No X
Unclear
1.16

Are confidence intervals for the absolute effect of the intervention presented

CI are not provided

 Yes
No X
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes X
No
Unclear
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Assessment

Selection Bias: High (1.4)

Performance and detection bias : Low

Attrition Bias: High (1.13)

Confusion Bias: High (1.14)

Other problems Yes

Overall Risk: Very high

Checklist for series of subjects exposed to intervention studies
Reference: Zhang XH, Xu J, Chen DQ, Guo LF, Qiu LQ. Effectiveness of treatment to improve pregnancy outcomes among women with syphilis in Zhejiang Province, China. Sex Transm Infect. 2016 Nov,92(7):537-541. doi: 10.1136/sextrans-2015-052363.
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

The purpose of this study was to determine the prevalence of maternal syphilis, treatment effectiveness and syphilis-associated pregnancy outcomes.

Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

All pregnant women with syphilis who delivered between 1 January 2013 and 31 December 2014 were enrolled. We recorded women’s pregnancy outcomes, including live births and perinatal deaths (still birth at >28 weeks and 0-7 days for neonatal deaths)

Yes X
No
Unclear
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

Women who terminated their pregnancies voluntarily, who had multiple pregnancies or suffered early miscarriage (<28 weeks) and without clear treatment information were excluded from the Study

 Yes X
No
Unclear
1.4

What proportion of eligible subjects participated in the study?

There is no information on the candidate population and exclusions

 Yes
No
Unclear X
1.5

Were exposed subjects included in strict sequential order?

Apparently, all mothers and newborns who met the inclusion criteria (3767)

Yes X
No
Unclear
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

Table 1

Yes X
No
Unclear
1.7

Is the intervention applied to the subjects clearly defined?

If women chose to continue pregnancies, they were provided free treatment with two courses of penicillin injections in the first rimester and the third trimester, respectively, such as 2.4 million units of benzathine penicillin by weekly injection for 3 weeks or 0.8 million units of procaine penicillin by daily injection for 15 days per treatment course. Erythromycin or ceftriaxone was provided to those women who were allergic to penicillin,

Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

We categorized women according to treatment regimens: whether treated or not, whether treated adequately or inadequately and the trimester of treatment initiation. The treated group included all women with syphilis who received at least one dose of penicillin/ erythromycin/ceftriaxone during pregnancy. Women who did not receive treatment during the entire pregnancy period were considered the untreated group. Women with two courses ofpenicillin injections and at least 2 weeks off between the two courses were categorised in the adequate treatment group. Others who received non-penicillin treatment or were treated with fewer than two courses were classified in the inadequate treatment group.

Yes X
No
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is no information

 Yes
No
Unclear X
1,10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open label study Hard outcomes

 Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

No Gestational age

No time between Treatment and delivery

Yes

No

Unclear
1.12

Are outcome variables adequately defined and measured?

CS was diagnosed in infants who met any one of the lollowingcriteria: (1) infants with a titre in the TRUST or RPR tests four or more times higher than his or her mother’s values during labour (however, the absence of a fourfold increase could not exclude CS); (2) infants with abnormal physical examinations consistent with syphilis infection; (3) infants with positive TPPA/TPHA tests lasting until 18 months after birth or (4) infants with positive IgM or T. pal lidum.

Yes X
No
Unclear
1.13

What proportion of subjects were lost to follow-up?

There were no losses

 Yes X
No
Unclear
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

There was no use of inference causal analysis

 Yes
No X
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

It is not relevant

 Yes
No
Unclear X
1.16

Are confidence intervals for the absolute effect of the intervention presented

CI 95% were calculated

 Yes X
No
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes X
No
Unclear
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Assessment

Selection Bias. Unclear

Performance and detection bias High (1.8)

Attrition Bias: Low

Confusion Bias: High

Other problems: CI 95% was not calculated

Overall Risk: Very high

Checklist for series of subjects exposed to intervention studies
Reference: Zhu L, Qin M, Du L, Xie RH, Wong T, Wen SW Maternal and congenital syphilis in Shanghai, China, 2002 to 2006. Int J Infect Dis. 2010 ;14 Suppl 3:e45-8. doi: 10.1016/j. ijid.2009.09.009
Checklist verified by:
Section 1 Internal validity
In this case series (exposed) study: (Please include the relevant excerpt from the evaluated study.) In this study the criterion is: (Mark the selected answer with an X)
1.1

Does the study define an appropriate, clear, and focused research question?

To assess the trends and determinants of maternal and congenital syphilis in Shanghai, China.

Yes X
No
Unclear
1.2

Is there a clear description of the inclusion criteria for subjects exposed to the intervention?

All pregnant women who had their prenatal care services provided by a hospital or a clinic in Shanghai and delivered their babies in Shanghai betweenJanuary1, 2002 and December31, 2006

 Yes
No
Unclear X
1.3

Is there a clear description of the exclusion criteria for subjects exposed to the intervention?

There is no information

 Yes
No
Unclear X
1.4

What proportion of eligible subjects participated in the study?

100%

 Yes X
No
Unclear
1.5

Were exposed subjects included in strict sequential order?

All women with GS were included

 Yes X
No
Unclear
1.6

Was a baseline measurement of the characteristics of the exposed subjects conducted to establish their condition prior to the intervention?

No description of Characteristics of women with GS

 Yes
No
Unclear X
1.7

Is the intervention applied to the subjects clearly defined?

For primary, secondary, and early latent syphilis, we used Benzhatine penicillin G (4.8 million units)

Intramuscularly in two doses (9.6 million units in total) weekly.

For late latent syphilis, we used benzathine penicillin G (2.4 million units) intramuscularly in three doses (7.2 million units in total)

Weekly.

Yes X
No
Unclear
1.8

Is the intervention described in sufficient detail to allow replication (definition and components)?

Maternal syphilis cases who received a whole course of penicillin treatment was considered completely treated, and those who did not complete a whole course of Treatment were considered incompletely treated.

Women with less or more of 28 weeks were compared

Do not take into account the effect of incomplete treatment on the incidence of SC

 Yes
No X
Unclear
1.9

Were any co-interventions applied differentially to the exposed subjects?

There is no information

 Yes
No
Unclear X
1.10

Were measures taken to prevent prior knowledge of exposure from influencing outcome assessment?

Open label study There is not a clear definitions of GS

 Yes
No X
Unclear
1.11

Are prognostic variables adequately defined and measured?

Gestational age

No time between Treatment and delivery

 Yes X
No
Unclear
1.12

Are outcome variables adequately defined and measured?

CS: Congenital syphilis is syphilis in an infant whose mother has transmitted the infection vertically to the foetus. Relevant demographic and clinical data for maternal syphilis and" congenital syphilis cases were collected using structured forms

 Yes
No X
Unclear
1.13

What proportion of subjects were lost to follow-up?

Apparently, there were no losses

 Yes
No
Unclear X
1.14

Are the main confounding factors identified and accounted for in the analysis (e.g., causal inference methods)?

Authors did no uses causal inference analysis

 Yes
No X
Unclear
1.15

Is there an estimation of the required sample size to determine the benefit of the intervention?

All base population was included

 Yes X
No
Unclear
1.16

Are confidence intervals for the absolute effect of the intervention presented

Not provided

 Yes
No X
Unclear
Section 2 - Overall Evaluation of the Study
2,1 Taking into account clinical considerations and your evaluation of the methodology used, do you consider that the observed effect is probably due to the investigated exposure? Yes
No
Unclear X
2,2 Are the results of the study directly applicable to the target population of the systematic review? Yes X
No
Unclear
Open in a new tab

Risk of Bias Assessment

Selection Bias: Unclear

Performance and detection bias: High

Attrition Bias: low

Confounding: High

Overall Risk: Very High

APPENDIX 6. RISK OF BIAS OF CASES SERIES (JBI TOOL)

APPENDIX 7. ADDITIONAL FIGURES

How to cite this article: Gutiérrez-Tamayo AM, Mirama-Calderón LV, Vallejo-Ortega MT, Gaitán-Duarte HG. Effectiveness of treating gestational syphilis in the last trimester on the incidence of congenital syphilis: a systematic review and meta-analysis. Rev Colomb Obstet Ginecol. 2025;76:4268. https://doi.org/10.18597/rcog.4268

Author contribution

AMGT and LVMC

contributed to protocol development, initial search, study selection, data extraction, and the writing and review of the final manuscript.

MTVO

contributed to the updated search, study selection, data extraction, analysis, and the writing and review of the final manuscript.

HGGD

contributed to protocol development, initial search, study selection, data extraction, analysis, and the writing and review of the final manuscript.

COMPETING INTEREST STATEMENT

AMTM, LVMC, and MTVO

declared that they have no conflicts of interest.

HGGD

declared a potential conflict of interest due to his position as Editor-in-Chief of the Colombian Journal of Obstetrics and Gynecology. He states that the manuscript was evaluated by three independent peer reviewers and that the journal’s standard editorial process was fully followed. The reviewers’ reports are available for inspection if required.

FUNDING

The project did not receive any funding.

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