Change in Cervical Length across Pregnancies and Preterm Delivery

Objective This study aimed to determine whether a decrease in midtrimester cervical length across pregnancies is associated with preterm delivery in a subsequent pregnancy. Study Design This is a cohort study of women who had two consecutive singleton births at the same institution. Midtrimester cervical length change across pregnancies was measured as the difference in centimeters (cm) between cervical lengths using the measurement taken closest to 20 (0/7) weeks' gestation in each pregnancy. Cervical length shortening was defined as present if the cervical length decreased by at least one standard deviation in the subsequent pregnancy. Results Among 1,552 women, 114 (7.4%) experienced a preterm delivery in the subsequent pregnancy. Compared with women whose subsequent pregnancy cervical length remained stable or increased, women whose cervical length shortened were more likely to experience a preterm delivery (10.3 vs. 6.7%; p = 0.04). Cervical length shortening remained associated with preterm delivery even when accounting for a woman's prior preterm delivery, prior pregnancy short cervix, interdelivery interval, progesterone use, and cervical length in the subsequent pregnancy (adjusted odds ratio = 1.89; 95% confidence interval = 1.11-3.20). Conclusion Midtrimester cervical length shortening across pregnancies is independently associated with an increased risk of preterm delivery.