Rebecca J. Baer, Christina D. Chambers, Kelli K. Ryckman, Scott P. Oltman, Larry Rand, Laura L. Jelliffe-Pawlowski

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 to a propensity score matched reference population. The sample was selected from California births in 2007-2012. STI 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. 16,312 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 <32 weeks due to preterm premature rupture of the membranes (PPROM) or provider-initiated birth (ORs 4.0-4.2). Women with gonorrhea were at increased odds of a preterm birth, a birth <32 weeks, or an early term birth (ORs 1.2-1.8). Chlamydia did not raise the odds of either a preterm or early term birth. 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.