Ultrasonographic cervical length measurement at 10-14 and 20-24 weeks gestation and the risk of preterm delivery

OBJECTIVE: To compare cervical length measurements at 10-14 and 20-24 weeks gestation in asymptomatic women with singleton pregnancies and to assess the measurements as a predictor of preterm delivery. STUDY DESIGN: In this prospective study, cervical length was measured in 152 asymptomatic women with singleton pregnancies using transvaginal ultrasonography at 10-14 and 20-24 weeks gestation. The primary outcome measure was spontaneous preterm delivery before 35 weeks of gestation. The mean cervical length was calculated at both stages, and lengths were compared between the term and preterm groups. RESULTS: The rate of spontaneous preterm deliveries was 10.5%. The mean cervical length at 10-14 and 20-24 weeks was 40.5 and 37.1mm, respectively. The cervical length at 10-14 weeks was not significantly different between those who delivered at term (40.9 mm) and those who delivered preterm (38.6 mm). By contrast, the cervical length at 20-24 weeks was significantly shorter in the group that had preterm deliveries (28.4 mm) than in those who had term deliveries (37.8 mm) (P < 0.001). The cervical shortening was more apparent in the group that delivered prematurely (from 38.6 to 28.4 mm) than in that which delivered at term (from 40.9 to 37.8 mm). CONCLUSION: Cervical length measurement used to predict preterm delivery was found to be more predictive at 20-24 weeks. Cervical length measurement at 10-14 weeks was not reliable for predicting preterm delivery. The mean cervical length tapered gradually from the first to the second scan, and the more rapid cervical shortening was found to be associated with increased risk for preterm delivery.