To estimate if the risk of spontaneous preterm birth (SPTB) associated with bacterial vaginosis (BV) is modified by three specific components of pregnancy history.
We performed a 4-year prospective cohort study of urban pregnant subjects who were universally screened for BV at <13 weeks with vaginal Gram stain and the Nugent criteria interpreted by a trained technician. The primary outcome was spontaneous preterm delivery (<37 weeks). Providers and investigators were blinded to the BV screen results. Data on multiple obstetric, medical and demographic variables were collected using a questionnaire, mid-pregnancy interview and postpartum chart review. Bivariable and multivariable statistical methods were used to assess the exposure-outcome association and pertinent interactions identified a priori: preterm premature rupture of membranes (PPROM), symptomatology, and antibiotic therapy.
Among 1826 enrolled patients, 1452 progressed beyond 22 weeks and had complete data. The prevalence of BV was 37% (n=537): 13% symptomatic and 24% asymptomatic. The prevalences of spontaneous and any preterm birth were 7.3% (n=106) & 11.4% (n=153), respectively. BV was not significantly associated with spontaneous preterm birth in the overall population in the unadjusted or multivariable analysis (Adjusted OR 0.8, 95%CI 0.5-1.2). However, the association between BV and SPTB was modified by pregnancy history, such that women with prior PPROM and current BV had a markedly increased odds of preterm birth compared to women with BV without prior PPROM (Interaction adjusted OR 8.3, 95%CI 1.5-47.6). The BV-SPTB association was not modified by symptomatology or prenatal antibiotic treatment.
In this general obstetric population, BV conveyed increased risk for spontaneous preterm birth only if preceded by a history of PPROM in a prior pregnancy. This interaction could be the result of genetic variation or environmental factors that predispose the high-risk patient to a hyper-inflammatory response to BV.
© 2008 Mosby, Inc. Published by Elsevier Inc. All rights reserved.