The effect of childbirth on hiatal dimensions.

OBJECTIVE To estimate changes in levator hiatal dimensions after childbirth in women with and without ultrasonographically visible morphological abnormalities of the levator ani and to correlate those changes with delivery mode. METHODS A total of 296 nulliparous women were recruited. They were examined with four-dimensional translabial ultrasonography at 36-38 weeks of gestation and at 3-4 months postpartum. Peripartal changes in levator hiatal dimensions were correlated with delivery data. RESULTS Mean postpartum follow-up was 5.3 months (median 4.1, interquartile range 3.7 to 5.1). Of 212 women who returned for follow-up, 101 had had normal vaginal deliveries (48%), 31 vacuum/forceps (15%), and 80 cesarean deliveries (38%). After cesarean delivery, there was a decrease in the mean hiatal area on Valsalva maneuver of 8.5% (P=.005). Vaginal delivery without avulsion was associated with an increase of 6% (P=.035). In women with avulsion injury, hiatal area increased by 28% (P=.002). Mean postpartum hiatal area on Valsalva was 25.46 cm after vaginal delivery with avulsion, 22.61 cm without avulsion, and 19.13 cm in the cesarean delivery group. After avulsion, hiatal area on contraction also increased significantly (P<.001). CONCLUSION Vaginal childbirth results in enlargement of the levator hiatus, especially after an avulsion. However, even without macroscopic levator trauma, there may be increased distensibility of the hiatus, which may be another mechanism leading to enlargement of the hiatus and pelvic organ prolapse. LEVEL OF EVIDENCE II.