Risk factors for spontaneous preterm birth are mediated through changes in cervical length

Although a short cervix in the mid-trimester of pregnancy is one of the strongest predictors of preterm birth (i.e., parturition before 37 completed weeks), there is limited understanding of how the dynamics of cervical remodeling (i.e., changes in cervical length) leading up to labor and delivery can inform obstetrical risk.

In this study, latent growth curve analysis was applied to serial cervical length measurements across pregnancy (median per subject = 6; IQR = 3-8) to quantify characteristics of cervical change in a cohort of 5111 singleton pregnancies carried by Black American women.

A conditional mediation model including nine common maternal risk factors of spontaneous preterm birth as exogenous predictors accounts for 26.5% of the variability in gestational duration. The collective evidence supports the conclusion that the effect of common maternal characteristics on spontaneous preterm birth is mediated through cervical length change. Specifically, previous preterm birth, pre-pregnancy BMI, parity, and previous abortion are shown to have unique influences on preterm birth risk that likely operate, in part, through linear changes in the cervix across pregnancy.

This study provides an account of the intermediary role of cervical dynamics in associations between known maternal risk factors and gestational age at delivery. Although these findings may not be generalizable to all populations, they have the potential to enhance screening efforts for women who are disproportionately affected by health disparities related to preterm birth.