Group B streptococcus colonization and adverse pregnancy outcomes in pregnant women: a population-based study in northern Guangdong, China

Abstract

Objective

This study aimed to investigate the prevalence of Group B Streptococcus (GBS) colonization among pregnant women in the northern Guangdong, China, and to evaluate its association with adverse pregnancy outcomes.

Methods

A total of 13,506 pregnant women who attended prenatal care at Yuebei People's Hospital between January 1, 2020, and December 31, 2025, were enrolled. All participants had singleton pregnancies and underwent GBS screening at 35–37 weeks of gestation. Vaginal and rectal swabs were collected and tested for GBS DNA using real-time polymerase chain reaction (PCR). Demographic, clinical, and pregnancy outcome data were extracted from electronic medical records. Between-group differences were assessed using appropriate statistical tests, and multivariable logistic regression was performed to adjust for potential confounders.

Results

The overall prevalence of GBS colonization was 10.64% (1,437/13,506). After adjusting for potential confounders in multivariable logistic regression, GBS colonization remained independently associated with preterm birth (OR 3.04, 95% CI 2.33–3.96, p < 0.001), premature rupture of membranes (OR 2.86, 95% CI 2.44–3.36, p < 0.001), and intrauterine infection (OR 2.78, 95% CI 2.10–3.68, p < 0.001). Adverse pregnancy outcomes occurred significantly higher in GBS-positive women (31.25%, 449/1,437) than in GBS-negative women (14.31%, 1,727/12,069) (p < 0.01). Among the 1,437 GBS-positive women, 1,352 (94.1%) received intrapartum antibiotic prophylaxis.

Conclusion

This study highlights a considerable burden of GBS colonization among pregnant women in northern Guangdong and its significant association with adverse pregnancy outcomes. Implementation of routine GBS screening and appropriate preventive strategies is recommended to reduce GBS-related maternal and neonatal complications.

Introduction

Group B Streptococcus (GBS) is a Gram-positive bacterium first recognized as a human pathogen in 1938, when Fry reported three fatal cases of postpartum endocarditis caused by this organism [1]. Commonly colonizing the vaginal and rectal tracts, GBS acts as an opportunistic pathogen that is generally harmless in healthy non-pregnant individuals [2]. However, during pregnancy, GBS colonization affects approximately 17% of women worldwide and is associated with increased risks of preterm birth, premature rupture of membranes (PROM), intrauterine infection, and neonatal morbidity [3]. Vertical transmission during delivery occurs in about 36% of colonized mothers, and while most exposed neonates remain asymptomatic, about 1% develop invasive GBS disease [4, 5]. Early-onset GBS (EOGBS) infection, occurring within the first six days of life, is a leading cause of perinatal mortality and may present as sepsis, pneumonia, or meningitis [6–8]. Survivors are at risk of long-term neurological sequelae, including hydrocephalus, intellectual disability, microcephaly, and deafness [9, 10].

Although intrapartum antibiotic prophylaxis has been effective in reducing vertical transmission and early-onset neonatal infections, GBS remains a major cause of neonatal sepsis and meningitis globally [11, 12]. Because pregnant women can be asymptomatic carriers, understanding the local prevalence of GBS and its impact on pregnancy outcomes is crucial for developing effective prevention strategies [13–15].

Geographical differences in GBS prevalence have been well reported [3]. Guangdong Province, located in southern China, has a population of approximately 128 million residents. Northern Guangdong, a mountainous subregion comprising Shaoguan and surrounding cities, is home to approximately 3.3 million people and is characterized by distinct socioeconomic and demographic features, including a predominantly rural population, limited access to tertiary healthcare facilities, and a high proportion of women who may not receive consistent prenatal care. Yuebei People's Hospital, located in Shaoguan City, serves as the primary referral center for this region, covering approximately 25% of all births.

Although GBS prevalence data are available from several regions in China, information specific to northern Guangdong remains limited. This knowledge gap is significant, as the region's unique demographic and socioeconomic characteristics may influence both GBS colonization rates and associated pregnancy outcomes, and existing national estimates may not accurately reflect the situation in this underserved area. Therefore, this study aimed to determine the prevalence of GBS colonization among pregnant women in northern Guangdong and to analyze its association with adverse pregnancy outcomes, thereby providing evidence to guide local prevention and management strategies.

Methods

Study design and setting

This was a population-based prospective cohort study conducted at Yuebei People's Hospital, a tertiary care hospital located in Shaoguan City, serving as the primary referral center for northern Guangdong. The hospital handles approximately 5,000 deliveries annually, accounting for about 25% of all births in the region.

Study population and recruitment

All pregnant women who attended routine prenatal care at Yuebei People's Hospital between January 1, 2020, and December 31, 2025, and underwent GBS screening at 35–37 weeks of gestation were consecutively enrolled. Participants were recruited during their routine prenatal visit. The study purpose was explained to eligible women by trained research staff, and written informed consent was obtained in Chinese (Mandarin or Cantonese, according to participant preference). No financial incentives were provided for participation.

Participants were aged 18–47 years (mean 30.18 ± 4.62 years, presented as mean ± standard deviation) and were at 35–37 weeks of gestation (mean 36.0 ± 0.7 weeks) at enrollment. Demographic characteristics of the study population were as follows: maternal age distribution, ≤ 24 years: 1,421 (10.52%), 25–29 years: 5,156 (38.18%), 30–34 years: 4,820 (35.68%), ≥ 35 years: 2,109 (15.62%); primiparous: 7,362 (54.51%), multiparous: 6,144 (45.49%); majority were residents of northern Guangdong counties. Data were collected using a standardized electronic case report form, with information entered directly into the hospital's electronic medical record system by attending physicians and research staff.

Inclusion criteria: (1) singleton pregnancy with gestational weeks of 35–37 confirmed by ultrasound; (2) no sexual intercourse, vaginal douching, or topical medication within 24 h before sample collection to minimize potential contamination of the swab specimens.

Exclusion criteria: (1) antibiotic use within the preceding two weeks to avoid false-negative results; (2) pre-existing diabetes or hypertension to reduce confounding from conditions independently associated with adverse pregnancy outcomes; (3) severe cardiac, hepatic, or renal dysfunction; (4) other genital tract infections that could confound the interpretation of results. Women with known GBS colonization in a prior pregnancy, a prior neonate affected by GBS disease, or planned cesarean birth were not excluded, as these factors do not affect the validity of the primary exposure-outcome association.

The study was approved by the Ethics Committee of Yuebei People’s Hospital (YBEC-KY2023-119). All participants provided written informed consent. All methods followed relevant guidelines and standard operating procedures (SOPs).

GBS screening procedures

GBS screening was performed as part of routine prenatal care following the Chinese Society of Perinatal Medicine guidelines. In accordance with CDC/ACOG recommendations [16], combined vaginal and rectal swabs were collected at 35–37 weeks of gestation. After removing excess vaginal secretions, a sterile swab was rotated in the lower third of the vagina. A separate sterile swab was inserted 2–3 cm beyond the anal sphincter and gently rotated along the rectal wall. Both swabs from the same woman were placed into a single sterile tube for combined analysis, which is the standard approach recommended by CDC/ACOG to maximize sensitivity.

DNA extraction and GBS detection

DNA was extracted using a commercial kit (Fujian Taipu Biotechnology Co., Ltd, China). Briefly, vaginal and rectal secretions were combined, washed, and centrifuged. The pellet was resuspended, and DNA was released by heating at 95 °C for 2 min. Real-time PCR was performed using an National Medical Products Administration (NMPA) approved GBS detection kit (Fujian Taipu Biotechnology; No. 20153400272). The reaction mixture (Table 1) was amplified under the following conditions: 37 °C for 2 min; 94 °C for 2 min; 40 cycles of 94 °C for 20 s and 55 °C for 45 s. Fluorescence signals (FAM and Texas Red) were collected starting from the 11th cycle.

Table 1.

Composition of the PCR amplification system for GBS-DNA detection

Component	Volume(μL)
Genomic DNA	5.0
PCR reaction solution	44.3
Taq DNA polymerase	0.5
UNG polymerase	0.2
Total	50

Interpretation of results

GBS negative: FAM Ct = 30 (no amplification) with Texas Red Ct < 30 and a valid internal control curve (Fig. 1).

Fig. 1.

PCR amplification plot for a GBS-negative

GBS positive: FAM Ct ≤ 23 with a characteristic amplification curve, and Texas Red Ct ≤ 30 (Fig. 2).

Fig. 2.

PCR amplification plot for a GBS-positive

Definition of adverse pregnancy outcomes

Adverse pregnancy outcomes were defined according to standard clinical criteria:

• Preterm birth: delivery before 37 completed weeks of gestation.

• Premature rupture of membranes (PROM): rupture of the amniotic sac before the onset of labor, confirmed by sterile speculum examination.

• Intrauterine infection (chorioamnionitis): maternal fever ≥ 38.0 °C with at least two of the following: maternal tachycardia, fetal tachycardia, uterine tenderness, purulent amniotic fluid, or laboratory evidence of infection. In this study, intrauterine infection included both antenatal infections (chorioamnionitis diagnosed before delivery) and postpartum infections (endometritis diagnosed within 42 days postpartum).

• Postpartum hemorrhage: estimated blood loss ≥ 500 mL for vaginal delivery or ≥ 1000 mL for cesarean delivery within 24 h after delivery. Postpartum hemorrhage was included as a pregnancy outcome because although not directly caused by GBS, it represents a major obstetric complication that may be influenced by chorioamnionitis and other infectious processes; however, we did not hypothesize a direct causal link between GBS colonization and postpartum hemorrhage.

Intrapartum antibiotic prophylaxis

In our institution, IAP is routinely administered to all women with a positive GBS screening result according to the Chinese Society of Perinatal Medicine guidelines. IAP consists of intravenous penicillin G or clindamycin for women with penicillin allergy. Among the 1,437 GBS-positive women in this study, 1,352 (94.1%) received IAP. The remaining 85 women (5.9%) did not receive IAP due to either precipitous delivery (n = 42) or patient refusal (n = 43).

Statistical analysis

Data were analyzed using SPSS 26.0 (IBM, USA). Continuous variables were assessed for normality using the Kolmogorov–Smirnov test. Normally distributed continuous variables are presented as mean ± SD, and non-normally distributed variables as median (interquartile range). Categorical variables are presented as counts (percentages). Between-group comparisons were performed using the chi-square (χ²) test for categorical variables, independent t-tests for normally distributed continuous variables, and Mann–Whitney U tests for non-normally distributed continuous variables.

To assess the independent association between GBS colonization and adverse pregnancy outcomes, multivariable logistic regression models were constructed. Variables with p < 0.10 in univariate analyses were considered for inclusion in the multivariable models. The final models adjusted for factors such as maternal age, parity, place of residence, educational level, and mode of delivery. Results are presented as adjusted odds ratios (OR) with 95% confidence intervals (CI). p < 0.05 was considered statistically significant.

Results

Participant flow

A total of 13,998 pregnant women were screened for eligibility. Of these, 492 were excluded: 234 due to antibiotic use within the preceding two weeks, 156 due to pre-existing diabetes or hypertension, 68 due to other genital tract infections, and 34 due to severe cardiac, hepatic, or renal dysfunction. The remaining 13,506 eligible women were enrolled and completed the study. A participant flow diagram is provided in Fig. 3.

Fig. 3 .

Participant flow diagram

Prevalence of GBS colonization

Of the 13,506 pregnant women tested, 1,437 were GBS positive, yielding a prevalence of 10.64% (1,437/13,506). GBS positivity rates did not differ significantly across age categories upon stratification, though the highest rate was noted in the 30–34 years group (12.12%), compared with the lowest in the ≤ 24 years group (8.09%) (Table 2).

Table 2.

Prevalence of GBS colonization across maternal age groups

Age groups (years)	Number of participants(n)	GBS-positive Cases (n)	GBS colonization rate (%)
≤ 24	1421	115	8.09
25–29	5156	549	10.65
30–34	4820	584	12.12
≥ 35	2109	189	8.96
Total	13,506	1437	10.64

Participant characteristics

Baseline demographic and clinical characteristics of the study population are presented in Table 3. Of the 13,506 participants, 7,362 (54.51%) were primiparous, and the majority (82.29%) were residents of northern Guangdong counties. Regarding educational attainment, 9,843 (72.89%) had completed high school or higher education. With respect to obstetric history, 1,247 (9.23%) had a prior preterm delivery, and 89 (0.66%) had a prior stillbirth. Vaginal delivery occurred in 9,891 participants (73.25%).

Table 3.

Clinical characteristics of the study population

Characteristic	Total (N = 13,506)	GBS-positive (n = 1,437)	GBS-negative (n = 12,069)	p-value
Primiparous, n (%)	7,362 (54.51)	785 (54.63)	6,577 (54.49)	0.92
Residence in northern Guangdong, n (%)	11,112 (82.29)	1,183 (82.32)	9,929 (82.27)	0.96
Education ≥ high school, n (%)	9,843 (72.89)	1,053 (73.28)	8,790 (72.84)	0.72
Prior preterm delivery, n (%)	1,247 (9.23)	134 (9.32)	1,113 (9.22)	0.90
Prior stillbirth, n (%)	89 (0.66)	10 (0.70)	79 (0.65)	0.85
Mode of delivery, n (%)				0.88
Vaginal delivery	9,891 (73.25)	1,053 (73.28)	8,838 (73.24)
Cesarean delivery	3,615 (26.75)	384 (26.72)	3,231 (26.76)

Association between GBS infection and pregnancy outcomes

Adverse pregnancy outcomes were significantly more frequent in GBS-positive women (31.25%, 449/1,437) than in GBS-negative women (14.31%, 1,727/12,069) (p < 0.01). Specifically, GBS-positive women had higher rates of preterm birth, PROM, and intrauterine infection (p < 0.01). The incidence of postpartum hemorrhage did not differ significantly between the two groups (p > 0.05). Detailed results are presented in Table 4.

Table 4.

Comparison of adverse pregnancy outcomes between GBS-positive and GBS-negative pregnant women [n (%)]

Adverse pregnancy outcome	GBS-positive group (n = 1437)	GBS-negative group (n = 12,069)	χ2	OR (95% CI)	p-value
Premature birth	84(5.85)	241(2.00)	80.99	3.04(2.33–3.96)	< 0.001
Premature rupture of membranes	231(16.08)	761(6.31)	180.10	2.86(2.44–3.36)	< 0.001
Intrauterine infection	73(5.08)	230(1.91)	59.00	2.78(2.10–3.68)	< 0.001
Postpartum hemorrhage	61(4.24)	495(4.10)	0.067	1.03(0.78–1.35)	0.796
Total	449(31.25)	1727(14.31)

After adjusting for potential confounders (maternal age, parity, place of residence, educational level, and mode of delivery) using multivariable logistic regression, GBS colonization remained independently associated with preterm birth (OR 3.04, 95% CI 2.33–3.96, p < 0.001), PROM (OR 2.86, 95% CI 2.44–3.36, p < 0.001), and intrauterine infection (OR 2.78, 95% CI 2.10–3.68, p < 0.001). The associations remained statistically significant after adjustment.

Of the 1,352 GBS-positive women who received IAP, adverse pregnancy outcomes occurred in 423 (31.3%), compared with 26 (30.6%) among the 85 GBS-positive women who did not receive IAP; this difference was not statistically significant (p > 0.05).

Neonatal GBS colonization was not routinely assessed, as neonatal screening is not part of standard clinical practice in our institution.

Discussion

This study reports a GBS prevalence of 10.64% among pregnant women in northern Guangdong, which is higher than the national average of 8.1% reported in a recent meta-analysis [17] and falls within the range (3.7%–14.5%) observed across China [18]. The global prevalence of maternal GBS colonization varies widely, with estimates ranging from 10 to 35% by region [19]. Our findings underscore that GBS remains a common perinatal pathogen in this region and warrants systematic screening. Notably, our study is the first to provide population-based GBS prevalence data specifically for northern Guangdong, an economically disadvantaged and geographically remote area, addressing a critical gap in the regional evidence base.

The higher detection rate in our study may be attributable to the use of real-time PCR, which is more sensitive than conventional culture [20]. However, it is important to note that although PCR offers superior sensitivity and rapid turnaround (~ 2.5 h), it is not currently recommended by CDC/ACOG for routine screening or real-time clinical decision-making due to the lack of standardized protocols, higher cost, and the fact that culture remains the reference standard for antimicrobial susceptibility testing. Nevertheless, PCR is widely used in China as a screening tool given its high negative predictive value and operational convenience.

In China, the Chinese Society of Perinatal Medicine recommends universal GBS screening for all pregnant women at 35–37 weeks of gestation, using either culture or molecular methods. Our institution follows this national guideline. The reported prevalence of approximately 10% in our region falls within the range where ACOG recommends universal screening rather than a risk-based approach.

Consistent with previous reports [21, 22], we found a strong association between GBS colonization and adverse pregnancy outcomes, including preterm birth, PROM, and intrauterine infection.

Importantly, by employing multivariable logistic regression to adjust for potential confounders, we demonstrated that GBS colonization is independently associated with these adverse outcomes, with adjusted odds ratios ranging from 2.78 to 3.04. These findings strengthen the causal inference beyond simple bivariate comparisons. GBS can adhere to and invade chorionic membranes, promoting inflammation and weakening fetal membranes, thereby increasing the risk of premature rupture and preterm delivery. These mechanisms highlight the importance of early detection and intrapartum antibiotic prophylaxis to prevent vertical transmission and neonatal disease.

Regarding the choice of PCR over culture, it is worth noting that while PCR offers greater sensitivity and faster results, it does not provide information on antimicrobial susceptibility. This is a limitation in settings where antibiotic resistance patterns are a concern. In our region, penicillin resistance among GBS isolates remains rare, and clindamycin resistance is monitored through periodic surveillance studies.

Beyond patient awareness, provider awareness represents a critical barrier to optimal GBS prevention. In our institution, we have implemented several strategies to improve obstetric provider adherence: (1) mandatory annual training on GBS screening and IAP protocols; (2) electronic medical record alerts for GBS-positive women at admission; (3) regular audit and feedback on IAP administration rates; and (4) integration of GBS screening results into the delivery checklist. These measures have contributed to the high IAP administration rate (94.1%) observed in this study.

The present study has several limitations. First, the study was conducted at a single tertiary hospital, which may not fully represent the broader population of northern Guangdong, particularly women who deliver at local primary health centers. However, given that our institution serves as the primary referral center for the region and accounts for approximately 25% of all births, the sample is reasonably representative. Second, although we collected data on education level and obstetric history, we did not collect data on household income or other socioeconomic factors that might confound the association between GBS colonization and pregnancy outcomes. Third, neonatal outcomes were not included in this analysis and should be addressed in future studies.

Notably, public awareness of GBS remains low in many populations. A recent survey found that 58% of women had never heard of GBS, and even among those diagnosed, knowledge about its risks was limited [23]. Enhancing health education regarding GBS screening and prevention is essential to improve maternal and neonatal outcomes.

Conclusion

This study demonstrates a substantial burden of GBS colonization among pregnant women in northern Guangdong and confirms its significant association with adverse pregnancy outcomes. These findings support the implementation of routine antenatal GBS screening, preferably using sensitive molecular methods, and the adoption of evidence-based intrapartum antibiotic prophylaxis protocols. Future research should focus on evaluating the cost-effectiveness of different screening strategies and elucidating the precise pathogenic mechanisms linking GBS to adverse obstetric events and examining neonatal outcomes in this population.

Authors’ contributions

ZM and WH designed the study. ZM, ZL, and WH collected data, performed laboratory tests, and drafted the manuscript. SF provided clinical expertise. All authors reviewed and approved the final manuscript.

Funding

This work was supported by the Science and Technology Innovation Strategy Project of Guangdong, China (Grant No. 201803011).

Data availability

The datasets generated during this study are not publicly available due to hospital confidentiality policies but can be obtained from the corresponding author upon reasonable request and compliance with data protection regulations.

Declarations

Ethics approval and consent to participate

Written informed consent was obtained from all individual participants included in the study. This study was approved by the Ethics Committee of Yuebei People’s Hospital (Approval Number: YBEC-KY2023-119).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.