An evaluation of sexually transmitted infection and odds of preterm or early term birth using propensity score matching.

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 to a propensity score matched reference population.

METHODS: 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.

RESULTS: 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.

CONCLUSION: 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.