434: How to Measure the Cervical Length: A Prospective Cohort Study in the Netherlands

Cervical length is an important predictor of spontaneous preterm birth. So far, the best way to measure cervical length has not been established. We aim to compare six methods of cervical length measurement to determine which technique is the best at predicting spontaneous preterm birth. We performed a prospective cohort study in women with a singleton pregnancy between August 2014 and December 2016. During the routine fetal anomaly scan (18-22 weeks) women were offered a transvaginal ultrasound for cervical length measurement to screen for the risk of spontaneous preterm birth. Each cervix was measured in six different ways: single-line, two-line (reference) and trace, with and without cervico-isthmic complex (CIC). We evaluated the predictive value of the different measurements for spontaneous delivery before 37 weeks using ROC curves. Our final study population comprised 508 women. The overall spontaneous preterm birth rate was 7.3%. The mean gestational age at measurement was 19+5 weeks. Median cervical length ranged from 40.0 mm to 49.0 mm for the different techniques (p=<0.001; Table 1). The area under the curve was 0.66 (95% CI 0.56-0.75) in the two-line without CIC, 0.63 (95% CI 0.52-0.73) in one-line without CIC and 0.65 (95% CI 0.56-0.75) in trace without CIC respectively. Using the measurement with CIC, the area under the curve was 0.66 (95% CI 0.54-0.78), 0.64 (95% CI 0.52-0.76) and 0.67 (95% CI 0.56-0.78) in two-line, one-line and trace respectively. While different measurement methods resulted in statistically significant differences in measured cervical length, this did not translate into clinically relevant better prediction of spontaneous preterm birth.