This cohort study of mother-infant dyads assesses whether children with prenatal exposure to azithromycin are at high risk of neurodevelopmental disorders compared with those exposed to other antibiotics or unexposed to any antibiotics during gestation.
Key Points
Question
What is the risk of neurodevelopmental disorders (NDDs) in children prenatally exposed to azithromycin compared with those exposed to β-lactams or unexposed to antibiotics during pregnancy?
Findings
In this cohort study of 15 527 mother-infant dyads, late pregnancy azithromycin exposure was associated with a lower incidence of composite NDDs compared with all other antibiotics and β-lactams, but no statistically significant difference was found compared with no prenatal antibiotic exposure.
Meaning
These findings suggest that late pregnancy azithromycin exposure may be associated with a lower incidence of NDDs compared with other antibiotics, but more research is needed.
Abstract
Importance
Azithromycin is commonly used during pregnancy to treat bacterial infections, but its effects on neurodevelopmental disorders (NDDs) remain inconclusive.
Objective
To evaluate the risk of NDDs in children prenatally exposed to azithromycin compared with those exposed to other antibiotics or with no antibiotic exposure during gestation.
Design, Setting, and Participants
This retrospective cohort study used data from an administrative health claims database (January 1, 2012, to October 31, 2024). The study evaluated a mother-infant cohort of mothers aged 12 to 55 years with a live birth between December 1, 2012, and December 31, 2023, who filled at least 1 prescription for an antibiotic or were unexposed to antibiotics during pregnancy. Mothers with antibiotic exposure within 90 days before pregnancy were excluded.
Exposures
Propensity scores were used to match children exposed to azithromycin with those exposed to other antibiotics or no antibiotics during the entire, early, and late pregnancy periods.
Main Outcomes and Measures
Cox proportional hazards regression models were applied to assess the incidence of NDDs, including attention-deficit/hyperactivity disorder, autism spectrum disorder, speech and language disorder (SLD), developmental coordination disorder, and behavioral disorders, during follow-up, in the azithromycin cohort compared with those exposed to other antibiotic classes or those with no antibiotic exposure.
Results
Among 15 527 mother-infant dyads (mean [SD] maternal age, 32.4 [4.1] years) included in this study, 742 (4.8%) were exposed to azithromycin, 3079 (19.8%) were exposed to other antibiotics, and 11 706 (75.4%) remained unexposed to antibiotics during pregnancy. After a mean (SD) follow-up of 5.5 (3.0) years, late pregnancy azithromycin exposure was associated with a lower risk of SLD compared with those unexposed (adjusted hazard ratio [AHR], 0.61; 95% CI, 0.39-0.94) as well as a lower risk of overall NDDs (AHR, 0.69; 95% CI, 0.49-0.98) and SLD (AHR, 0.59; 95% CI, 0.39-0.91) compared with those exposed to other antibiotics.
Conclusions and Relevance
In this cohort study, late pregnancy azithromycin exposure was associated with a lower risk of NDDs, particularly SLDs. However, azithromycin prescribing during pregnancy should remain guided by clinical necessity and existing safety recommendations; further studies using larger and more diverse populations are warranted to confirm these findings.
Introduction
Azithromycin, a second-generation macrolide antibiotic, is commonly used during pregnancy to treat bacterial infections, including sexually transmitted diseases, toxoplasmosis, malaria, and respiratory infections in patients allergic to penicillins.1,2,3,4 Approximately 37% of women in the US use antibiotics during pregnancy, and 3% use azithromycin.5,6 Although fetal plasma concentrations of azithromycin reach approximately 2.6% of maternal circulating levels after transplacental transfer,7,8 the drug remains widely used as an alternative to erythromycin for antibiotic prophylaxis in preterm premature rupture of membranes.9,10,11 It is also used as adjunctive prophylaxis for cesarean and vaginal deliveries,12 with evidence showing a reduction in surgical site infections for the former and lower rates of maternal sepsis and mortality for the latter.13,14,15,16,17 Some observational studies18,19,20 have reported an association between azithromycin use during pregnancy and spontaneous abortion (SAB); however, data on its effects on birth outcomes remain inconsistent. Many studies have suggested no association between major congenital malformations (MCMs) or adverse birth outcomes with azithromycin use during the first or third trimester of pregnancy,21,22,23,24,25,26,27,28,29,30 whereas others have reported an increased risk of MCMs.31,32,33
Azithromycin exerts its antibacterial effects by binding to the 50S ribosomal subunit and inhibiting protein synthesis34 and induces mitochondrial dysfunction, reactive oxygen species overproduction, DNA oxidative damage, upregulation of the HIF1A (OMIM 603348) gene, and aerobic glycolysis in healthy mammalian cells,35 suggesting a potential for adverse effects on neurodevelopment. In contrast, neuroprotective effects of azithromycin have been demonstrated in animal models.36,37,38,39 Animal studies37,40 have shown that azithromycin modulates the inflammatory reaction and microglial activation to reduce apoptosis and preserve retinal ganglion cells. However, the effects of azithromycin use on neurodevelopmental outcomes in children remain undetermined. Evidence on whether fetal exposure to azithromycin is associated with the risk of neurodevelopmental disorders (NDDs), which occur in approximately 24% of publicly insured children in the US and have been linked to the use of certain prescription medications during pregnancy, remains limited.41,42 Therefore, this study evaluates the risk of NDDs in children with prenatal exposure to azithromycin compared with those exposed to other antibiotics or unexposed to any antibiotics during gestation to provide evidence to inform safer antibiotic selection in pregnancy.
Methods
Data Source
This cohort study used patient-level administrative claims data from commercially insured individuals in the New England region of the US. The data consist of eligibility information, inpatient and outpatient encounters, and pharmacy dispensing claims for commercial health plan enrollees from January 1, 2012, to October 31, 2024. This longitudinal dataset, spanning 13 years, is beneficial for assessing NDDs that develop in children several years after birth. The institutional review board at the University of Rhode Island granted an exemption for this study and waived the requirement for informed consent because the study data were deidentified. This study adhered to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cohort studies.
Study Design
This retrospective cohort study used propensity score (PS) methods. The index date was the pregnancy start date, estimated using the last menstrual period. The baseline period, defined as 90 days of continuous insurance coverage prior to pregnancy, was used to assess demographic and clinical characteristics. A schematic representation of the study design is shown in the Figure.
Figure. Study Design Flowchart.
NDD indicates neurodevelopmental disorder.
Study Cohort
The study cohort included linked mother-infant dyads, with mothers aged 12 to 55 years who had a live birth between December 1, 2012, and December 31, 2023. Validated algorithms were used to link mother-infant dyads and define pregnancy episodes and gestational age.43,44 Mother-infant dyads were included if mothers were dispensed at least 1 prescription for any antibiotic or remained unexposed to antibiotics during pregnancy. In addition, mothers were required to have continuous insurance enrollment from the baseline period through the entire pregnancy to ensure accurate definitions of exposure and covariates, whereas infants were required to be enrolled in insurance within 90 days of birth to facilitate outcome assessment during the follow-up period. Mother-infant dyads were excluded based on the following criteria: (1) mothers exposed to teratogenic medications during pregnancy (eTable 1 in Supplement 1), (2) mothers or infants diagnosed with chromosomal abnormalities during baseline or pregnancy, (3) mothers with no antibiotic exposure during the pregnancy period but who used antibiotics during the baseline, and (4) mothers who were dispensed multiple antibiotic classes during pregnancy. The eFigure in Supplement 1 illustrates the cohort selection process according to the inclusion and exclusion criteria.
Exposure Assessment
Early pregnancy is considered a critical window for medication-related cognitive risks. Nevertheless, evidence from clinical and animal studies indicates that late pregnancy exposure may also affect offspring cognitive development.45,46 Thus, we assessed the risk of NDDs with azithromycin exposure during 3 pregnancy periods: (1) entire pregnancy (from pregnancy start date to delivery date), (2) early pregnancy only (from pregnancy start date to 20 weeks of gestation), and (3) late pregnancy only (from 20 weeks of gestation to delivery date). Exposure was characterized by at least 1 dispensed prescription for monotherapy azithromycin or any other antibiotic at any point during pregnancy (eTable 2 in Supplement 1). Antibiotics were identified using generic drug names and National Drug Codes available in the pharmacy claims data.
Outcome Assessment
Neurodevelopmental outcomes assessed in this study included attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), speech and language disorder (SLD), developmental coordination disorder, and behavioral disorder, identified using a validated algorithm based on International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) and International Statistical Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes from inpatient and outpatient claims (eTable 3 in Supplement 1).47 To address the co-occurrence and possible shared underlying mechanisms among these outcomes, we defined the primary outcome as a composite of any of the investigated NDDs and the secondary outcomes as those specific NDDs.48 Children were followed up from delivery until the occurrence of an NDD diagnosis, loss of insurance coverage, or the study’s end date on October 31, 2024.
Covariates
Prespecified potential confounding factors included maternal age at delivery, obstetric factors (ie, mode of delivery, calendar year of delivery, gestational age, and singleton or multiple gestations), maternal infections during pregnancy, and maternal comorbidities, including hypertension, diabetes, autoimmune diseases, asthma, depression, anxiety, epilepsy, ADHD, bipolar disorder, schizophrenia, and psychosis. Additional confounders considered were maternal concomitant medication use, including benzodiazepines, antidepressants, anticonvulsants, antidiabetics, antipsychotics, stimulants, steroids, antihypertensives, acetaminophen, nonsteroidal anti-inflammatory drugs, and opioids. Health care resource use, measured by the number of hospital visits and antibiotic prescriptions filled during pregnancy, was also accounted for, along with child sex.49,50,51,52,53,54,55,56,57
Statistical Analysis
A 1:1 nearest-neighbor PS matching with a caliper of 0.01 was used to achieve balance in baseline characteristics between treatment groups. Descriptive statistics for all covariates were evaluated and compared between comparison groups before and after adjusting by PS matching, and the results were presented using standardized mean differences. Because analyses were conducted across multiple exposure windows, PSs were recalculated and matching was repeated separately within each analytic cohort, including subgroup and sensitivity analyses, before outcome modeling. Cox proportional hazards regression models were applied to assess the association between azithromycin exposure and the incidence of NDDs compared with exposure to other systemic antibiotics or no antibiotic exposure during pregnancy. The proportional hazards assumption was verified through Schoenfeld residual tests. To account for correlations within the matched cohort, the robust sandwich variance estimator was used.58 Additionally, based on the definitions of the exposure period and outcomes, associations were analyzed for early, late, and entire pregnancy periods as well as for primary and secondary outcomes. Multiple comparison adjustments were not performed in this study to avoid inflated type II errors.59,60 All statistical analyses were conducted using SAS software, version 9.4 (SAS Institute Inc), with statistical significance set at a 2-sided P < .05.
Children exposed to other antibiotics were restricted to those exposed to β-lactams, which were further subclassified into penicillin and nonpenicillin β-lactam–exposed groups. The risk of NDDs associated with azithromycin exposure was compared with that of the β-lactam–exposed group and then with each β-lactam subclass to assess any potential intraclass difference in the risk of NDDs due to differences in chemical structure.
Respiratory tract infections (RTIs) represent one of the most common shared indications for azithromycin and penicillin β-lactams. We therefore conducted sensitivity analyses on mothers treated for RTIs within the groups exposed to azithromycin, penicillin, or β-lactam to allow for the assessment of potential class-specific differences in NDD risk associated with a common clinical indication. We also conducted sensitivity analyses restricted to children born before 2020 to address potential temporal confounding related to the COVID-19 pandemic and secular trends in SLD diagnoses. The analyses were repeated using PS fine stratification with strata of 50 to confirm the robustness of the results obtained in the primary analyses that used PS matching to adjust for confounders.
Results
Of the total 15 527 mother-infant dyads (mean [SD] maternal age, 32.4 [4.1] years) included in this study, 742 (4.8%) were exposed to azithromycin, 3079 (19.8%) to other antibiotics, and 11 706 (75.4%) remained unexposed to antibiotics during pregnancy. Baseline characteristics of the study population were similar among all comparison groups except calendar year of birth and the baseline use of opioid analgesics. More children exposed to azithromycin during gestation were born between the years 2012 and 2019 compared with the other comparison groups. Similarly, opioid analgesic use during the baseline period was more common among azithromycin-exposed mothers than among those in the other exposure groups. RTIs were the most common infections during pregnancy in all exposure groups (Table 1). Baseline characteristics and other covariates were balanced between azithromycin and all the other comparison groups after PS matching (eTables 4-8 in Supplement 1).
Table 1. Baseline Characteristics of Study Population Before Propensity Score Adjustment.
| Characteristic | No. (%) of participantsa | ||||
|---|---|---|---|---|---|
| Azithromycin users (n = 742) | Unexposed cohort (n = 11 706) | All other antibiotics users (n = 3079) | β-Lactam users (n = 1832) | Penicillin β-lactam users (n = 1449) | |
| Maternal age, mean (SD), y | 32.8 (4.7) | 32.4 (4.1) | 32.3 (4.2) | 32.5 (4.1) | 32.8 (4.0) |
| Antibiotic indication | |||||
| Respiratory tract infections | 387 (52.2) | 2776 (23.7) | 810 (26.3) | 827 (45.1) | 770 (53.1) |
| Urinary tract infections | 25 (3.4) | 642 (5.5) | 373 (12.1) | 127 (6.9) | 51 (3.5) |
| Other infectionsb | 66 (8.9) | 3640 (31.1) | 468 (15.2) | 286 (15.6) | 199 (13.7) |
| Year of birth | |||||
| 2012-2019 | 679 (91.5) | 8437 (72.1) | 2362 (76.7) | 1393 (76.0) | 1138 (78.5) |
| 2020-2024 | 63 (8.5) | 3269 (27.9) | 717 (23.3) | 439 (24.0) | 311 (21.5) |
| Obstetric conditions | |||||
| Preterm birth | 11 (1.5) | 60 (0.5) | 18 (0.6) | 5 (0.3) | 3 (0.2) |
| Cesarean delivery | 281 (37.9) | 3628 (31.0) | 1105(35.9) | 637 (34.8) | 521 (36.0) |
| Multiple gestation | 102 (13.7) | 1052 (9.0) | 246 (8.0) | 130 (7.1) | 90 (6.2) |
| No. of hospital visits with infection | |||||
| 1 | 241 (32.5) | 2802 (23.9) | 998 (32.4) | 630 (34.4) | 509 (35.1) |
| 2 | 154 (20.8) | 950 (8.1) | 616 (20.0) | 421 (23.0) | 343 (23.7) |
| 3 | 84 (11.3) | 357 (3.0) | 296 (9.6) | 192 (10.5) | 150 (10.4) |
| ≥4 | 116 (15.6) | 371 (3.2) | 354 (11.5) | 221 (12.1) | 184 (12.7) |
| Total No. of antibiotic prescriptions | |||||
| 1 | 531 (71.6) | NA | 2306 (74.9) | 1488 (81.2) | 1153 (79.6) |
| 2 | 143 (19.3) | NA | 520 (16.9) | 264 (14.4) | 228 (15.7) |
| ≥3 | 68 (9.2) | NA | 252 (8.2) | 80 (4.4) | 68 (4.7) |
| Child sex | |||||
| Male | 379 (51.1) | 5870 (50.1) | 1561 (50.7) | 898 (49.0) | 720 (49.7) |
| Female | 363 (48.9) | 5836 (49.9) | 1518 (49.3) | 934 (51.0) | 729 (50.3) |
| Maternal baseline comorbidities | |||||
| Hypertension | 11 (1.5) | 95 (0.8) | 37 (1.2) | 21 (1.1) | 17 (1.2) |
| Diabetes | 6 (0.8) | 56 (0.5) | 22 (0.7) | 13 (0.7) | 11 (0.8) |
| Asthma | 27 (3.6) | 204 (1.7) | 80 (2.6) | 50 (2.7) | 41 (2.8) |
| Depression | 68 (9.2) | 736 (6.3) | 252 (8.2) | 158 (8.6) | 119 (8.2) |
| Anxiety | 67 (9.0) | 861 (7.4) | 317 (10.3) | 193 (10.5) | 150 (10.4) |
| ADHD | 10 (1.3) | 142 (1.2) | 52 (1.7) | 24 (1.3) | 20 (1.4) |
| Bipolar disease | 18 (2.4) | 165 (1.4) | 59 (1.9) | 37 (2.0) | 32 (2.2) |
| Autoimmune disease | 16 (2.2) | 228 (1.9) | 83 (2.7) | 49 (2.7) | 40 (2.8) |
| Maternal baseline drug use | |||||
| Benzodiazepines | 51 (6.9) | 379 (3.2) | 166 (5.4) | 99 (5.4) | 84 (5.8) |
| Antidepressants | 115 (15.5) | 1123 (9.6) | 453 (14.7) | 290 (15.8) | 231 (15.9) |
| Anticonvulsants | 35 (4.7) | 215 (1.8) | 108 (3.5) | 75 (4.1) | 59 (4.1) |
| Stimulants | 19 (2.6) | 219 (1.9) | 86 (2.8) | 49 (2.7) | 37 (2.6) |
| Steroids | 36 (4.9) | 215 (1.8) | 99 (3.2) | 66 (3.6) | 57 (3.9) |
| Antihypertensives | 14 (1.9) | 158 (1.3) | 62 (2.0) | 30 (1.6) | 26 (1.8) |
| Antidiabetics | 15 (2.0) | 178 (1.5) | 86 (2.8) | 47 (2.6) | 37 (2.6) |
| Acetaminophen | 4 (0.5) | 42 (0.4) | 18 (0.6) | 14 (0.8) | 10 (0.7) |
| NSAIDs | 37 (5.0) | 295 (2.5) | 120 (3.9) | 70 (3.8) | 60 (4.1) |
| Opioids | 71 (9.6) | 410 (3.5) | 200 (6.5) | 130 (7.4) | 110 (7.6) |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; NA, not applicable: NSAIDS, nonsteroidal anti-inflammatory drugs.
Unless otherwise indicated.
Other infections include vaginitis, sexually transmitted infections, ear infections, and skin infections merged into a composite category due to small sample size.
Results of the Cox proportional hazards models after a mean (SD) follow-up time of 5.5 (3.0) years showed no significant differences in the risk of overall NDDs among children exposed to azithromycin compared with those unexposed to antibiotics during any of the exposure periods. A lower risk of SLD was, however, observed with late pregnancy azithromycin exposure compared with no antibiotic exposure (adjusted hazard ratio [AHR], 0.61; 95% CI, 0.39-0.94). Although a lower risk of ASD (AHR, 0.37; 95% CI, 0.14-0.96) was observed among children exposed to azithromycin at any time during pregnancy compared with those unexposed, the low event count suggests that the significant estimate may be attributable to chance (Table 2).
Table 2. Risks of NDDs in the Exposure Periods: Azithromycin vs Unexposed.
| NDD type | Anytime during pregnancy (n = 1066) | Early pregnancy only (≤20 weeks’ gestation) (n = 538) | Late pregnancy only (>20 weeks’ gestation) (n = 578) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Azithromycin, No. of events (n = 533) | Unexposed, No. of events (n = 533) | AHR (95% CI)a | Azithromycin, No. of events (n = 269) | Unexposed, No. of events (n = 269) | AHR (95% CI) a | Azithromycin, No. of events (n = 289) | Unexposed, No. of events (n = 289) | AHR (95% CI) a | |
| Any NDD | 111 | 117 | 0.89 (0.69-1.16) | 63 | 67 | 0.86 (0.61-1.21) | 52 | 70 | 0.71 (0.49-1.01) |
| Autism | NR | 15 | NA | NR | 12 | 0.47 (0.17-1.24) | NR | NR | NA |
| ADHD | 17 | 19 | 0.75 (0.39-1.45) | NR | 14 | 0.52 (0.22-1.22) | NR | NR | 1.08 (0.42-2.82) |
| DCD | 27 | 36 | 0.74 (0.45-1.22) | 12 | 22 | 0.52 (0.26-1.04) | 13 | 17 | 0.76 (0.37-1.56) |
| Speech and language disorder | 74 | 86 | 0.82 (0.60-1.12) | 46 | 48 | 0.90 (0.60-1.35) | 33 | 51 | 0.61 (0.39-0.94) |
| Behavioral disorder | 14 | 11 | 1.18 (0.54-2.58) | NR | NR | 1.16 (0.46-2.93) | 11 | NR | 1.53 (0.59-3.94) |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; AHR, adjusted hazard ratio; DCD, developmental coordination disorder; NA, not applicable (hazard ratio is extreme or implausible values); NDD, neurodevelopmental disorder; NR, not available (data censored for counts fewer than 11).
AHRs were estimated using unexposed pregnancies as the reference group.
No significant difference in the risk of any of the NDDs was observed in children exposed to azithromycin and those exposed to other antibiotics during the entire or early pregnancy periods. Late pregnancy exposure analysis, however, showed a significantly lower risk of composite NDDs (AHR, 0.69; 95% CI, 0.49-0.98) and SLD (AHR, 0.59; 95% CI, 0.39-0.91) in azithromycin-exposed children compared with those who were exposed to other antibiotics (Table 3).
Table 3. Risks of NDDs in the Various Exposure Periods: Azithromycin vs All Other Antibiotics.
| NDD type | Anytime during pregnancy (n = 1484) | Early pregnancy only (≤20 weeks’ gestation) (n = 662) | Late pregnancy only (>20 weeks’ gestation) (n = 570) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Azithromycin, No. of events (n = 742) | All other antibiotics, No. of events (n = 742) | AHR (95% CI)a | Azithromycin, No. of events (n = 331) | All other antibiotics, No. of events (n = 331) | AHR (95% CI)a | Azithromycin, No. of events (n = 285) | All other antibiotics, No. of events (n = 285) | AHR (95% CI)a | |
| Any NDD | 163 | 180 | 0.87 (0.70-1.08) | 84 | 76 | 1.18 (0.87-1.61) | 54 | 74 | 0.69 (0.49-0.98) |
| Autism | 14 | 15 | 0.90 (0.44-1.88) | NR | NR | NA | NR | NR | NR |
| ADHD | 29 | 27 | 0.98 (0.58-1.65) | 13 | 11 | 1.27 (0.57-2.82) | 10 | 16 | 0.59 (0.26-1.31) |
| DCD | 37 | 42 | 0.88 (0.56-1.37) | 18 | 14 | 1.35 (0.67-2.71) | 13 | 10 | 1.30 (0.57-2.96) |
| Speech and language disorder | 110 | 130 | 0.83 (0.64-1.07) | 58 | 57 | 1.08 (0.75-1.55) | 34 | 55 | 0.59 (0.69-0.91) |
| Behavioral disorder | 32 | 33 | 0.93 (0.57-1.51) | 15 | 12 | 1.36 (0.64-2.90) | 11 | 14 | 0.76 (0.35-1.68) |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; AHR, adjusted hazard ratio; DCD, developmental coordination disorder; NA, not applicable (hazard ratio is extreme or implausible values); NDD, neurodevelopmental disorder; NR, not available (data censored for counts fewer than 11).
AHRs were estimated using unexposed pregnancies as the reference group.
Results of the analyses comparing azithromycin with β-lactam antibiotics were consistent with those comparing azithromycin with other antibiotics. No significant difference was found between the 2 exposure groups during the entire and early pregnancy periods, but a significantly lower risk of composite NDDs (AHR, 0.62; 95% CI, 0.43-0.87) and SLD (AHR, 0.61; 95% CI, 0.39-0.94) was found in late pregnancy (Table 4).
Table 4. Risks of NDDs in the Various Exposure Periods: Azithromycin vs β-Lactams.
| NDD type | Anytime during pregnancy (n = 1424) | Early pregnancy only (≤20 weeks’ gestation) (n = 630) | Late pregnancy only (>20 weeks’ gestation) (n = 562) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Azithromycin, No. of events (n = 712) | β-Lactams, No. of events (n = 712) | AHR (95% CI)a | Azithromycin, No. of events (n = 315) | β-Lactams, No. of events (n = 315) | AHR (95% CI)a | Azithromycin, No. of events (n = 281) | β-Lactams, No. of events (n = 281) | AHR (95% CI)a | |
| Any NDD | 160 | 186 | 0.85 (0.69-1.05) | 80 | 71 | 1.17 (0.85-1.61) | 53 | 77 | 0.62 (0.43-0.87) |
| Autism | 14 | 19 | 0.75 (0.38-1.49) | NR | NR | NA | NR | 11 | NA |
| ADHD | 29 | 35 | 0.84 (0.51-1.38) | 13 | 17 | 0.87 (0.43-1.79) | NR | 13 | 0.67 (0.29-1.55) |
| DCD | 36 | 32 | 1.14 (0.71-1.83) | 17 | 13 | 1.36 (0.67-2.79) | 13 | 15 | 0.85 (0.40-1.77) |
| Speech and language disorder | 108 | 124 | 0.87 (0.67-1.12) | 54 | 47 | 1.19 (0.81-1.76) | 33 | 50 | 0.61 (0.39-0.94) |
| Behavioral disorder | 32 | 39 | 0.83 (0.52-1.33) | 16 | 16 | 1.02 (0.50-2.05) | 11 | 16 | 0.62 (0.29-1.32) |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; AHR, adjusted hazard ratio; DCD, developmental coordination disorder; NA, not applicable (hazard ratio is extreme or implausible values); NDD, neurodevelopmental disorder; NR, not available (data censored for counts fewer than 11).
AHRs were estimated using unexposed pregnancies as the reference group.
Compared with penicillin β-lactams, late-pregnancy azithromycin exposure was associated with a lower risk of composite NDDs and SLD (eTable 9 in Supplement 1), with similar findings in analyses restricted to mothers treated for RTIs (eTable 10 in Supplement 1). Comparisons with nonpenicillin β-lactams are not shown due to limited sample size, but results suggest similar directional findings.
Sensitivity analyses restricting the cohort to children born before the COVID-19 pandemic yielded results consistent with the primary analyses (eTables 11-14 in Supplement 1). Results of the sensitivity analyses using PS fine stratification for confounding adjustment showed similar results to the primary analysis and the various subgroup analyses (eTables 15-18 in Supplement 1).
Discussion
This study examined the risk of NDDs in children with prenatal azithromycin exposure compared with children unexposed to antibiotics or those exposed to other antibiotics during gestation. The findings indicate that azithromycin use after 20 weeks of gestation may be associated with a lower risk of NDDs compared with no antibiotic exposure and use of β-lactam antibiotics, particularly penicillins. Previous studies have reported conflicting findings on the association between gestational azithromycin or macrolide exposure and the risk of adverse pregnancy and birth outcomes.19,21,31,61 Although some observational studies have suggested no increased risk of SAB and MCMs with fetal exposure to azithromycin or macrolides,21,61 others have reported elevated risks of SAB, preterm birth, low birth weight, and MCMs, particularly involving the cardiovascular and digestive systems with early pregnancy macrolide exposure.20,25,31,62 Given these uncertainties, a commentary article recommended cautious prescribing of azithromycin during pregnancy.22 Although etiologically distinct from neurodevelopmental sequelae, these outcomes underscore the biological plausibility and multifactorial nature of fetal responses to antibiotic exposure.
Azithromycin possesses antiviral, immunomodulatory, and anti-inflammatory properties, including the ability to reduce the production of proinflammatory cytokines,63,64,65 which may partly explain the initial interest in its use for the management of patients with SARS-CoV-2 infection, although this has been refuted by previous studies.66,67 Excessive maternal or early-life inflammation, possibly from infections, has been linked to an increased risk of ASD and other adverse neurodevelopmental outcomes in offspring.68,69,70,71,72,73 Animal studies74,75,76 have also suggested that maternal immune activation is the causal link between maternal infection and ASD in offsprings. Anti-inflammatory or regulatory cytokines may, therefore, help to protect brain development, although the underlying mechanism is complicated by the critical balance between pro- and anti-inflammatory cytokines.77
Findings from previous studies on neurodevelopmental risks associated with fetal antibiotic exposure have been inconsistent.78,79,80,81 Compared with other antibiotics, including penicillin and nonpenicillin β-lactams, azithromycin has a longer half-life and better anti-inflammatory properties.82 These pharmacologic differences may contribute to the lower risk of NDDs observed in the azithromycin-exposed group relative to other antibiotic classes.
The late pregnancy period is characterized by rapid brain growth, synapse formation, and neural network refinement.83 Reducing inflammatory signaling during this period could plausibly provide neuroprotective effects. This may help explain the lower risk of composite NDDs and SLD in children prenatally exposed to azithromycin compared with other systemic antibiotics or no exposure after 20 weeks of gestation because accumulating evidence indicates that neurodevelopmental outcomes may be susceptible to late pregnancy exposures.41,84 Many animal studies examining the effects of medications on the brain have used neonatal rats, whose brain maturity is comparable to that of a human fetus in the third trimester.85 Azithromycin use during late pregnancy, particularly predelivery, has shown benefits for reduced infection, sepsis, and death in mothers, whereas similar effectiveness has not been observed in children.17,86,87 Although animal research has suggested that late pregnancy azithromycin exposure may lead to intrauterine growth retardation,88 human research has not reported similar adverse outcomes, except for vomiting and edema.87 Moreover, azithromycin-resistant infections in both mothers and infants may be a concern for gestational azithromycin use.22,89,90
The well-established safety profile of β-lactam antibiotics, particularly penicillins, makes them suitable for the treatment of bacterial infections during pregnancy.91 The immunomodulatory and anti-inflammatory properties of azithromycin may, however, confer additional neuroprotection in children with prenatal exposure relative to those exposed to penicillins. The results of our study showed no difference in the risk of ASD and ADHD between azithromycin and penicillins in all exposure periods. These findings are partially consistent with those of a study conducted using data from the Clinical Practice Research Datalink in the UK, which compared the risk of ASD and ADHD in children prenatally exposed to macrolides vs penicillins.31 Although the UK study31 evaluated macrolides as a class, our analysis focused specifically on azithromycin, a subclass of macrolides. Notably, azithromycin accounted for more than 96% of all macrolide prescriptions in our study population; therefore, our findings are likely reflective of the broader class-level results observed in the UK study.
Strengths and Limitations
This study has several strengths. First, we evaluated the association between prenatal azithromycin exposure and a broader range of NDDs using data from a community setting. Second, the study used an active comparator design, comparing azithromycin with other systemic antibiotic classes, including β-lactams, to minimize confounding by indication and enhance the validity of the comparative safety estimates. Third, the multiyear longitudinal nature of the data allowed for sufficient follow-up to capture NDDs. Fourth, robust confounding control was achieved through PS methods that adjusted for a broad range of maternal, perinatal, and health care use factors. Fifth, the use of validated NDD outcomes with high positive predictive values enhances the reliability of the findings. Sixth, the assessment of NDD risks across different pregnancy windows enabled identification of potential periods of exposure during which fetal neurodevelopment may be most responsive to the effects of azithromycin.
This study also has limitations. First, PS methods are limited to measurable covariates, leaving the potential for residual confounding from unmeasured factors, such as maternal diet, infection severity, or socioeconomic conditions. This study used claims data from a commercially insured population, which generally reflects a more homogeneous socioeconomic profile due to the employment-based nature of coverage. As such, substantial differences in socioeconomic status across exposure groups are less likely, and direct measures of socioeconomic factors were not available in the data for adjustment. Confounding by indication is also likely minimized by the use of active comparators. Obesity, although relevant, was excluded due to its poor sensitivity in administrative claims data; however, given the modest magnitude of its expected effect, this is unlikely to have substantially altered the study results. Second, exposure misclassification is possible because prescription dispensing may not necessarily reflect actual medication intake. Third, familial or genetic confounding could not be accounted for because sibling-comparison analyses were not feasible. Fourth, evaluation of a dose-response relationship was not feasible because azithromycin prescribing in this population showed little variability. Fifth, the analytic cohort was limited to pregnancies resulting in live births; thus, pregnancies resulting in fetal death, miscarriage, or SAB, which may represent competing outcomes or share underlying etiologic pathways with NDDS, were not captured, potentially leading to selection bias. Sixth, because the data were derived from a commercially insured population, the findings may not be generalizable to uninsured or publicly insured populations. Additionally, the relatively smaller sample size of azithromycin-exposed pregnancies, compared with β-lactam or unexposed groups, may have limited the power to detect small but clinically meaningful associations, especially for specific NDD subtypes.
Conclusions
In this observational cohort study, late pregnancy azithromycin exposure was associated with a lower risk of NDDs, especially SLD. However, azithromycin prescribing during pregnancy should be approached with caution and interpreted within the context of existing guidelines that recommend β-lactams as the preferred agents. Additional studies using larger and more diverse populations are warranted to confirm these results.
eFigure. Flow Chart of Study Cohort Selection
eTable 1. List of Potential Teratogenic Agents Excluded from the Analysis
eTable 2. Classes of Antibiotics used in the Analyses
eTable 3. Algorithm definitions and ICD-9 & ICD-10 codes for neurodevelopmental disorders
eTable 4. Baseline Characteristics of Study Population after Propensity Score Matching (Exposure at Any time During Pregnancy)
eTable 5. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs Unexposed)
eTable 6. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs All Other Antibiotics)
eTable 7. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs β-lactams)
eTable 8. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs Penicillin β-lactams)
eTable 9. Adjusted Hazard ratios for NDDs in the Various Exposure Periods (Azithromycin vs Penicillin β-lactams)
eTable 10. Adjusted Hazard ratios for NDDs in the Various Exposure Periods (Azithromycin vs Penicillin β-lactams in Patients with Respiratory Tract Infections – Propensity Score Matching)
eTable 11. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs All Other Antibiotics)
eTable 12. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs β-lactams)
eTable 13. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs Penicillin β-lactams)
eTable 14. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs Unexposed)
eTable 15. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs All Other Antibiotics)
eTable 16. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs β-lactams)
eTable 17. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs Penicillin β-lactams)
eTable 18. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs Unexposed)
Data Sharing Statement
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eFigure. Flow Chart of Study Cohort Selection
eTable 1. List of Potential Teratogenic Agents Excluded from the Analysis
eTable 2. Classes of Antibiotics used in the Analyses
eTable 3. Algorithm definitions and ICD-9 & ICD-10 codes for neurodevelopmental disorders
eTable 4. Baseline Characteristics of Study Population after Propensity Score Matching (Exposure at Any time During Pregnancy)
eTable 5. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs Unexposed)
eTable 6. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs All Other Antibiotics)
eTable 7. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs β-lactams)
eTable 8. Baseline Characteristics of Study Population Before and After Propensity Score Matching In Early and Late Pregnancy Periods (Azithromycin vs Penicillin β-lactams)
eTable 9. Adjusted Hazard ratios for NDDs in the Various Exposure Periods (Azithromycin vs Penicillin β-lactams)
eTable 10. Adjusted Hazard ratios for NDDs in the Various Exposure Periods (Azithromycin vs Penicillin β-lactams in Patients with Respiratory Tract Infections – Propensity Score Matching)
eTable 11. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs All Other Antibiotics)
eTable 12. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs β-lactams)
eTable 13. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs Penicillin β-lactams)
eTable 14. Sensitivity Analyses: Adjusted Hazard ratios for NDDs in in Children Exposed Prior to the Year 2020 Using Propensity Score Matching (Azithromycin vs Unexposed)
eTable 15. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs All Other Antibiotics)
eTable 16. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs β-lactams)
eTable 17. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs Penicillin β-lactams)
eTable 18. Adjusted Hazard ratios for NDDs in the Various Exposure Periods Using Propensity Score Fine Stratification, Strata=50 (Azithromycin vs Unexposed)
Data Sharing Statement
