microRNA expression in the cervix during pregnancy is associated with length of gestation.

Preterm birth is a leading cause of infant mortality and can lead to poor life-long health and adverse neurodevelopmental outcomes. The pathophysiologic mechanisms that precede preterm labor remain elusive, and the role that epigenetic phenomena play is largely unstudied. The objective of this study was to assess the association between microRNA (miRNA) expression levels in cervical cells obtained from swabs collected during pregnancy and the length of gestation. We analyzed cervical samples obtained between 16 and 19 weeks of gestation from 53 women in a prospective cohort from Mexico City, and followed them until delivery. Cervical miRNA was extracted and expression was quantified using the NanoString nCounter Analysis System. Linear regression models were used to examine the association between miRNA expression levels and gestational age at delivery, adjusted for maternal age, education, parity, body mass index, smoke exposure, and inflammation assessed on a Papanicolaou smear. We identified 6 miRNAs that were significantly associated with gestational age at the time of delivery, including miR-21, 30e, 142, 148b, 29b, and 223. Notably, per each doubling in miR-21 expression, gestations were 0.9 (95% CI: 0.2-1.5) days shorter on average (P = 0.009). Per each doubling in miR-30e, 142, 148b, 29b, and 223 expression, gestations were shorter by 1.0 to 1.6 days. The predicted targets of the miRNAs were enriched for molecules involved in DNA replication and inflammatory processes. The levels of specific miRNAs in the human cervix during pregnancy are predictive of gestational age at delivery, and should be validated in future studies as potential biomarkers of preterm birth risk.