Background: Few studies have examined the relationship between sexually transmitted infections (STIs) and preterm birth (<37 weeks gestation) by subtype (<32 weeks, 32-36 weeks, spontaneous, provider-initiated). Here, we evaluate the odds of preterm (by subtype) and early-term (37 and 38 weeks gestation) birth in women with an STI compared with a propensity score-matched reference population.
Methods: The sample was selected from California births in 2007 to 2012. Sexually transmitted infection was defined as a maternal diagnosis of chlamydia, gonorrhea, or syphilis in the birth certificate or hospital discharge record. A reference sample of women without an STI was selected using exact propensity score matching on maternal factors. Odds of preterm and early-term birth were calculated.
Results: Sixteen thousand three hundred twelve women were identified as having an STI during pregnancy and an exact propensity score-matched control was identified for 97.2% (n = 15,860). Women with an indication of syphilis during pregnancy were at 1.6 times higher odds of having a preterm birth and, in particular, at elevated odds of a birth less than 32 weeks due to preterm premature rupture of the membranes or provider-initiated birth (odds ratios 4.0-4.2). Women with gonorrhea were at increased odds of a preterm birth, a birth less than 32 weeks, or an early-term birth (odds ratios 1.2-1.8). Chlamydia did not raise the odds of either a preterm or early-term birth.
Conclusions: Gonorrhea and syphilis increased the odds of a preterm birth. Gonorrhea also increased the odds of an early-term birth. Chlamydia did not raise the odds of an early birth.