To assess the impact of parity and different delivery modes on the thickness of the puborectalis (PR).

A total of 150 postpartum women who visited the hospital 42~60 days after childbirth were selected between April and December 2019. The participants were divided into three groups according to parity and delivery modes: 50 women in a first vaginal delivery group, 50 in a second vaginal delivery group, and 50 in a cesarean section group. Two dimensional transperineal ultrasound examination was performed in all participants both at rest and in maximal contraction status. The thicknesses of the anterior, middle, and posterior parts of the PR were measured and analyzed by variance analysis among the three groups, and t test was used to analyze the differences between groups.

At rest, the thicknesses of the anterior, middle, and posterior parts of the PR in both sides of the first and second vaginal delivery groups were significantly thinner than those of the cesarean section group [left: (5.66±1.22) mm and (6.05±1.05) mm vs (6.73±1.30) mm, t=4.244 and 2.877, P＜0.001 and P=0.005, (5.88±1.22) mm and (6.11±1.12) mm vs (6.71±1.08) mm, t=3.602 and 2.727, P＜0.001 and P=0.008, (5.96±1.13) mm and (6.15±0.94) mm vs (6.72±1.21) mm, t=3.246 and 2.631, P=0.002 and P=0.010, respectively; right: (5.88±1.34) mm and (5.80±1.16) mm vs (6.49±0.96) mm, t=2.617 and 3.240, P=0.010 and P=0.002, (6.14±1.38) mm and (6.10±0.95) mm vs (6.81±0.91) mm, t=2.866 and 3.816, P=0.005 and P＜0.001, (6.22±1.30) mm and (6.10±1.15) mm vs (7.01±1.22) mm, t=3.133 and 3.838, P=0.002 and P＜0.001, respectively]. In maximal contraction status, the thicknesses of the anterior, middle, posterior parts of the PR in both sides of the first vaginal delivery group were significantly thinner than those of the cesarean section group [left: (6.83±1.30) mm vs (7.76±1.25)mm, t=3.646, P＜0.001, (7.00±1.42) mm vs (7.72±1.05) mm, t=2.883, P=0.005, (7.09±1.36) mm vs (7.83±1.28) mm, t=2.802, P=0.005, respectively; right: (7.11±1.35) mm vs (7.70±1.20) mm, t=2.192, P=0.031, (7.17±1.25) mm vs (7.89±1.20) mm, t=2.310, P=0.023, (7.33±1.36) mm vs (8.01±1.45) mm, t=2.419, P=0.017, respectively], but there was no statistical difference between the second vaginal delivery group and the cesarean section delivery group [left: (7.32±1.20) mm, (7.28±1.27) mm, and (7.56±1.35) mm; right: (7.23±1.19) mm, (7.44±1.22) mm, and (7.51±1.09) mm, respectively; P＞0.05 for all). There was also no statistical difference between the first and second vaginal delivery groups both at rest and in maximal contraction status (P＞0.05 for all).

It is the first vaginal delivery that is most likely to affect the contraction function of the PR, and cesarean section provides protection on the contraction function of the PR.