Risk Factors for Spontaneous Preterm Birth are Mediated through Changes in Cervical Length

Although short cervical length in the mid-trimester of pregnancy is a 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 of 6; IQR = 3-8) to quantify characteristics of cervical change in a cohort of 5,111 singleton pregnancies consisting predominantly of Black women. A conditional mediation model including nine common maternal risk factors for spontaneous preterm birth as exogenous predictors accounted for 26.5% of the variability in gestational age at delivery (P < 0.001). This model provides insight into distinct mechanisms by which specific maternal risk factors influence preterm birth. For instance, effects of maternal parity and smoking status were fully mediated through cervical change parameters, whereas the influence of previous preterm birth was only partially explained, suggesting alternative pathways could be involved. This study provides the first account of the intermediary role of cervical dynamics in associations between known maternal risk factors and gestational age at delivery.