Parity and gestational age are associated with vaginal microbiota composition in term and late term pregnancies

Abstract Vaginal microbiota and its potential contribution to preterm birth has been under intense research in recent years. However, only few studies have studied vaginal microbiota in later stages of pregnancy or at the onset of labor. We analyzed vaginal swab samples collected between 37- and 42-weeks of gestation from 324 Finnish women before elective cesarean section, at the onset of spontaneous labor, and in pregnancies continuing beyond 41 weeks of gestation. Vaginal microbiota composition associated strongly with parity, i.e. previous deliveries, and advancing gestational age. Absence of previous deliveries was a strong predictor of L. crispatus dominated vaginal microbiota, and the relative abundance of L. crispatus was higher in late term pregnancies, especially among nulliparous women. The results underscore the importance of the vaginal microbiota for improving the currently limited understanding on how the duration of gestation and timing of birth is regulated, with potentially vast clinical utilities.