Association between levator hiatal dimensions on ultrasound during first pregnancy and mode of delivery

To determine the association between levator hiatal dimensions, measured using transperineal ultrasound, in women during their first pregnancy and the subsequent mode of delivery, stratified by the indication for intervention.

In this prospective observational study, 280 nulliparous women with a singleton pregnancy were invited for transperineal ultrasound examination at 12 and 36 weeks' gestation. Their levator hiatal dimensions were measured at rest, on pelvic floor muscle contraction and on Valsalva maneuver. The subsequent mode of delivery was classified into five categories: spontaneous vaginal delivery, instrumental vaginal delivery owing to fetal distress, instrumental vaginal delivery owing to failure to progress, Cesarean section owing to fetal distress and Cesarean section owing to failure to progress. Levator hiatal dimensions according to mode of delivery were compared by analysis of variance and Tukey's post-hoc test. Since multiple comparison tests were performed, the statistical significance level was corrected using the Bonferroni method.

Of the 252 women included, those who delivered by Cesarean section because of failure to progress had a significantly smaller levator hiatal transverse diameter on pelvic floor contraction at 12 weeks' gestation than did women who had a spontaneous vaginal delivery (Tukey's post-hoc test, P < 0.001). There was also a trend towards a smaller hiatal area on pelvic floor contraction at 12 weeks' gestation in women who delivered by Cesarean section because of failure to progress compared to women who had a spontaneous vaginal delivery (Tukey's post-hoc test, P = 0.005). In women who had an instrumental vaginal delivery because of failure to progress there was a trend towards a smaller levator hiatal anteroposterior diameter on pelvic floor contraction at 36 weeks' gestation compared with women who had a spontaneous vaginal delivery (Tukey's post-hoc test, P = 0.033).

Smaller levator hiatal dimensions on pelvic floor contraction during first pregnancy are associated with a subsequent instrumental vaginal delivery or a Cesarean section owing to failure to progress.