Chlamydia trachomatis Is Associated With Medically Indicated Preterm Birth and Preeclampsia in Young Pregnant Women.

Background: Studies on Chlamydia trachomatis-associated pregnancy outcomes are largely conflicting, ignoring the heterogeneous natures of pregnancy complications and potential effect modification by maternal age. This study determined if prenatal C. trachomatis infection is associated with preterm birth (PTB) and preeclampsia subtypes.

Methods: A retrospective cohort study was conducted using 22,772 singleton pregnancies with a prenatal C. trachomatis diagnostic test. Spontaneous and medically indicated PTBs, and term and preterm preeclampsia were outcomes. Modified Poisson regression calculated relative risk (RR) and 95% confidence intervals (CI) with propensity score adjustments stratified by maternal ages <25 and ≥25 years.

Results: Overall, C. trachomatis was significantly associated with term preeclampsia (adjusted RR [RRadj], 1.88; 95% CI, 1.38-2.57). Among young women (age <25 years), C. trachomatis was significantly associated with medically indicated PTB (RRadj, 2.29; 95% CI, 1.38-3.78) and term preeclampsia (RRadj, 1.57; 95% CI, 1.05-2.36) in propensity-adjusted models. No significant associations in older women were detected.

Conclusion: C. trachomatis was associated with medically indicated PTB and term preeclampsia in young women. Associations between chlamydia and perinatal outcomes may depend on the subtype of PTB and preeclampsia, which should be investigated through mechanistic studies.