Association Between Maternal Chlamydia Infection and Gestational Age at Delivery- A Time-to-Event Analysis

Background Preterm birth is a leading cause of neonatal morbidity and mortality worldwide. Maternal infections, including Chlamydia trachomatis, have been linked to adverse pregnancy outcomes, yet their influence on the timing of delivery remains unclear. Most studies have examined preterm birth as a binary outcome, overlooking the variations in gestational age. This study evaluates the association between maternal Chlamydia trachomatis infection and gestational age at delivery using time-to-event analysis in a large, population-based cohort. Methods This retrospective cohort study utilized data from the National Vital Statistics System (NVSS) in the United States, comprising singleton live births from January 1, 2021, to December 31, 2023. Maternal Chlamydia infection during pregnancy was identified from standardized electronic birth records. Following 1:4 propensity score matching on key maternal and neonatal covariates, 171,695 Chlamydia-exposed pregnancies were compared with 686,780 unexposed controls. Cox proportional hazards models were used to estimate hazard ratios and 95% confidence intervals for preterm birth (< 37 weeks), early preterm birth (< 34 weeks), very preterm birth (< 32 weeks), and extremely preterm birth (< 28 weeks). Logistic regression models evaluated secondary outcomes including low birthweight and neonatal intensive care unit admission. Results Prenatal Chlamydia exposure was associated with a modest but statistically significant increased risk of preterm birth before 37 weeks (HR 1.07, 95% CI 1.06–1.09). Elevated risks were also observed for early preterm birth before 34 weeks (HR 1.10, 95% CI 1.07–1.13) and very preterm birth before 32 weeks (HR 1.07, 95% CI 1.03–1.12). No significant association was identified for extremely preterm birth before 28 weeks (HR 1.04, 95% CI 0.97–1.11). Secondary outcomes demonstrated higher odds of NICU admission and assisted ventilation in Chlamydia-exposed infants. Subgroup analyses showed generally consistent associations across maternal and neonatal characteristics. Conclusion Maternal Chlamydia trachomatis infection is associated with an increased hazard of early delivery, particularly at earlier gestational ages. These findings emphasize the need for targeted prenatal screening and timely treatment to reduce infection related risks for preterm birth and improve perinatal outcomes.