Is Transabdominal Sonography of the Cervix After Voiding a Reliable Method of Cervical Length Assessment?

Objective. The purpose of this study was to assess the correlation and agreement between transvagi‐nal and transabdominal cervical length measurement after bladder emptying as well as the feasibility of transabdominal sonography in cervical length screening. Methods. This was a prospective cohort study involving 287 participants (14–34 weeks' gestation) from January to December 2003. After voiding, transabdominal and transvaginal cervical length measurements were obtained. The optimal trans‐abdominal technique was established during an unblinded series of transabdominal and transvaginal cervical length measurements (n = 96). The same measurements were obtained in 191 participants under a blinded 2‐sonographer protocol. The transabdominal cervical length cutoff to ensure 100% sensitivity in detecting a short cervix (≤2.5 cm) was determined. Results. There was no difference between mean transabdominal and transvaginal cervical lengths ± SD (3.57 ± 0.74 versus 3.61 ± 0.74 cm; P = .20). The Pearson correlation coefficient was 0.824. The 95% tolerance interval for any paired observation (transabdominal minus transvaginal) was ?0.92 to 0.84 cm. All transvaginal cervical lengths of 2.5 cm or less were associated with paired transabdominal cervical lengths of 3 cm or less. Conclusions. With an optimal sonographic technique, postvoid transabdominal cervical measurement shows a close correlation and agreement with transvaginal assessment and is useful for cervical length screening.