To observe the effect of parity and delivery mode on levator hiatus (LH) area evaluated by pelvic floor three-dimensional ultrasound, and to explore their relationship with pelvic organ prolapse (POP).

A total of 250 postpartum women at 42~60 days after childbirth were selected at the Material and Child Health Hospital of Hubei Province from April to December 2019, including 150 first vaginal delivery (FVD) women, 50 second vaginal delivery (SVD) women, and 50 cesarean section (CS) women. The change of LH area was observed at rest and on maximal Valsalva maneuver by pelvic floor three-dimensional ultrasound. And 120 undelivered women were selected as a control group. The detection rate of POP by pelvic floor ultrasound in each group was analyzed. All the subjects were divided into a POP group (n=167) and a non-POP group (n=203) according to whether they had POP or not. The LH area was compared between groups at rest and on maximal Valsalva maneuver. ANOVA was used to compare LH area among different groups. The t-test was used to compare LH between the POP group and non-POP group. The difference of POP detection rate between different groups was analyzed by the χ² test.

The LH areas at rest in the SVD group, FVD group, CS group, and control group were (16.59±3.12) cm², (15.34±3.50) cm², (13.09±2.78) cm², and (11.09±2.47) cm², respectively; the corresponding values on maximal Valsalva maneuver were (22.80±8.37) cm², (18.46±6.63) cm², (15.58±3.91) cm², and (13.11±5.30) cm², respectively. The LH area both at rest and on maximal Valsalva maneuver differed significantly among the groups (F=31.89 and 11.14, respectively, P＜0.001), with the SVD group having the greatest values, followed by the FVD group, CS group, and control group. The detection rates of POP by pelvic floor ultrasound were 17.5%, 26.0%, 60.0%, and 86.0% in the control group, CS group, FVD group, and SVD group, respectively; although there was no significant difference between the CS group and control group, the differences between the following groups were statistically significant: SVD group vs FVD group (χ²=11.38, P＜0.001); SVD group vs CS group (χ²=36.53, P＜0.001); SVD group vs control group (χ²=70.55, P＜0.001); FVD group vs CS group (χ²=17.36, P＜0.001); FVD group vs control group (χ²=49.74, P＜0.001). The LH areas in the POP group were significantly larger than those in the non-POP group both at rest [(14.88±3.49) cm² vs (12.38±2.17) cm², t=8.06, P＜0.001] and on maximal Valsalva maneuver [(20.93±6.53) cm² vs (15.59±3.50) cm², t=9.50, P＜0.001].

Different delivery modes and parity have different effects on the LH area. The larger the area, the greater the risk of POP. Three-dimensional ultrasound can measure the LH area of postpartum women in different states, so as to detect the change of pelvic floor structure early.