Three-dimensional magnetic resonance imaging assessment of levator ani in women progressing from full-term pregnancy to 10months postpartum.

Abstract

To identify the anatomical morphology of levator ani (LA) in primigravidae at term pregnancy and its natural process of changing after delivery. Forty-one primigravidae (vaginal delivery: 29 women, cesarean delivery in the first stage of labor: 12 women) underwent magnetic resonance imaging (MRI) at full-term pregnancy, 6 weeks and 10months postpartum. Three-dimensional (3-D) model of LA created from MRI data using Mimics v.21.0 software and source images were assessed to determine the morphology. LA volume (LVOL) was calculated and used as indicator of muscle atrophy. Decrease of levator hiatus length (LH-L) was shown in both groups since 6 weeks postpartum. In the vaginal delivery group, the differences in LVOL between time points were significant (p < 0.05), showing a persistent decreasing tendency. Puborectalis attachment width (PAW) on the left was the smallest at 6 weeks postpartum (p < 0.05). LA avulsion and significant 2-D morphological change after delivery were only observed in this group (p < 0.05); In the cesarean section group, smaller LVOL was found at 6 weeks postpartum comparing with full-term pregnancy (p < 0.05); Larger levator-symphysis gap (LSG) and levator hiatus width (LH-W), smaller PAW were observed in vaginal delivery group comparing with cesarean section group at 6 weeks postpartum (p < 0.05), but none of the values exhibited between-group differences (p > 0.05) at 10months postpartum. No other comparisons were considered significant (p >0.05). Vaginal delivery, or even active labor itself may both lead to LA atrophy. And the morphology of LA is basically similar in different delivery modes at 10months postpartum once the onset of labor has occurred, even though it changes more complicatedly after vaginal delivery.