The reliability of transabdominal cervical length measurement in a low-risk obstetric population: Comparison with transvaginal measurement.

OBJECTIVE:To determine the correlation between transabdominal (TA) and transvaginal (TV) cervical length measurement in a low-risk obstetric population in Taiwan. MATERIALS AND METHODS:Women with a singleton pregnancy between 20 weeks and 24 weeks of gestation underwent postvoid TA and TV cervical length measurements. Differences between the measurements obtained using the two methods were evaluated. RESULTS:Two hundred and five women agreed to participate in the study. Paired TA and TV measurements were obtained in 174 women. The mean TA cervical length was 36.0 ± 4.9 mm and the mean TV cervical length was 37.6 ± 5.4 mm. The mean TA cervical length was shorter than the mean TV cervical length by 1.6 mm. The 5(th) percentile of TA and TV cervical length was 29 mm and 29.1 mm, respectively. The discrepancies between the two methods were not significantly correlated with maternal body mass index (BMI). All women with TV cervical length <25 mm had a corresponding TA cervical length <29 mm. CONCLUSION:The TA cervical length could be obtained in the majority of the low-risk pregnant women in the present study, and the TA cervical length was closely correlated with the TV cervical length. The use of TA ultrasound could be an effective initial tool for cervical length screening in low-risk pregnant women. TA cervical length <29 mm (5(th) percentile) could be used as a cut-off value for further TV ultrasound.