Impact of mode of delivery on levator morphology: a prospective observational study with three-dimensional ultrasound early in the postpartum period

Objective: To evaluate morphology and integrity of the levator ani muscle (LAM) with three-dimensional ultrasound early in the postpartum period.

Design: Prospective cross-sectional observational study.

Setting: University hospital in Germany.

Population: Women after vaginal delivery and caesarean section with no previous vaginal delivery.

Methods: Three-dimensional perineal ultrasound was performed between 48 and 72 hours postpartum. The axial plane at the level of minimal hiatal dimension and tomographic ultrasound imaging were used to determine LAM biometry and defect.

Main outcome measures: Primary outcome was to compare hiatal dimensions and levator defect following vaginal delivery or caesarean section. For secondary outcomes, we evaluated the role of caesarean section in protecting levator integrity, and the possible involvement of the first stage of labour in LAM changes.

Results: In all, 157 women participated: 81 (51.6%) following vaginal delivery (70 spontaneous and 11 operative deliveries) and 76 (48.4%) following caesarean section (55 elective and 21 emergency caesarean sections). All biometric indices of the levator were higher after vaginal delivery (P<0.001), except for LAM thickness. LAM defects were found to be significantly associated with vaginal delivery, with relative risk 7.5 (P<0.001). Following vaginal delivery, 32 (39.5%) levator defects were found: 27 (38.5%) after spontaneous delivery and five (45.4%) after operative delivery. Four (5.2%) women had a levator defect following emergency caesarean section.

Conclusion: Vaginal delivery modifies and damages the LAM: the risk of levator defect after vaginal delivery is more than seven times higher than after caesarean section. Despite this, emergency caesarean section seems to have no complete preventive effect on LAM trauma.