The effect of mode of delivery on pelvic floor functional anatomy

The objective of this study is to investigate and compare the effects of different modes of delivery on urethral sphincter volume, bladder neck mobility, and changes to levator hiatus distensibility using ultrasound imaging. This study is a prospective observational cohort study. The setting of this study is at a London teaching hospital. The population is composed of 156 women recruited in their first ongoing pregnancy. Primigravid women were recruited between 32 weeks and term. Antenatal ultrasound measurements of levator hiatus and bladder neck mobility were assessed at rest, maximum strain, and maximum valsalva using transvaginal ultrasound imaging. Urethral sphincter volume was calculated using a three-dimensional transvaginal probe. The investigations were repeated at 6 weeks and at 6 months postpartum. Total urethral sphincter volume, rhabdosphincter volume, bladder neck position at rest, and rotational mobility from maximum contraction to maximum valsalva were measured in this study. Levator hiatus area at rest and levator hiatus on valsalva and squeeze were also measured. The 156 women underwent antenatal ultrasound pelvic floor assessment. One hundred ten (71%) completed the 6-month follow-up. There were no differences in the urethral sphincter volume between the different modes of delivery. Overall, the urethral sphincter was smaller after delivery compared to the third trimester. Vaginal delivery was associated with a significantly larger levator hiatus area on valsalva antenatally and at rest, squeeze, and valsalva postnatally compared to caesarean section. Antenatal and postpartum bladder neck mobility was also significantly greater in the women who delivered vaginally. Urethral sphincter changes postpartum are independent of mode of delivery. Vaginal delivery is strongly associated with a larger, more distensible levator hiatus and a greater degree of bladder neck mobility both antenatally and postpartum.