Cervical Length Changes From the First to Second Trimester of Pregnancy, and Prediction of Preterm Birth by First‐Trimester Sonographic Cervical Measurement

Abstract

OBJECTIVES: The purpose of this study was to examine the evolution of cervical length from the first to second trimester of pregnancy and the value of first-trimester cervical measurement in the prediction of preterm delivery. METHODS: We conducted a longitudinal prospective study. Cervical length was measured by transvaginal sonography at 11 to 14 weeks (Cx1), 16 to 19 weeks (Cx2), and 20 to 24 weeks (Cx3). RESULTS: Eight hundred singleton pregnancies were studied. The median cervical lengths were 33 mm for Cx1 and 31 mm for Cx2 and Cx3. Significant independent predictors for cervical length were maternal weight, height, and history of cervical surgery for Cx1, maternal height, history of cervical surgery, and history of preterm delivery for Cx2, and history of cervical surgery, history of first-trimester miscarriage, and history of spontaneous preterm delivery for Cx3. Mean cervical length shortening was 2.36 mm between Cx1 and Cx3. In the subgroups of women with previous cervical surgery and history of previous preterm birth, cervical shortening was significantly more prominent. The median Cx1 was significantly shorter in the women who subsequently delivered preterm; Cx1 predicted preterm delivery before 34 weeks (odds ratio, 0.746; 95% confidence interval, 0.649-0.869) and preterm delivery before 32 weeks (odds ratio, 0.734; 95% confidence interval, 0.637-0.912). CONCLUSIONS: Cervical length in the first trimester depends on maternal characteristics and a history of cervical surgery. The cervix exhibits minimal changes from 11 to 24 weeks for most women, although the shortening is more prominent in women with a history of cervical surgery or preterm delivery. First-trimester cervical length measurement can predict preterm delivery.