How common is pelvic floor muscle atrophy after vaginal childbirth?

Objective To determine if there is evidence of levator ani atrophy in primiparous women. Methods This was a prospective observational cohort study of 202 primiparous women recruited between November 2006 and March 2008. Translabial ultrasound volumes were obtained at 36-38 weeks' gestation and at a mean of 4.5 months postpartum. Peripartum changes in bladder neck elevation and reduction of anteroposterior hiatal diameter on pelvic floor muscle contraction (PFMC) and changes in muscle thickness were analyzed. Results Of the 202 participants enrolled, 158 (78%) completed the study. There was a significant reduction in bladder neck elevation (P = 0.001) and change in anteroposterior hiatal diameter (P = 0.03) on PFMC when comparing antenatal and postnatal results, the latter being significantly associated with delivery mode (P = 0.013). No significant changes were detected in muscle thickness (P = 0.76). Conclusions There is a reduction in sonographic measures of pelvic floor function after childbirth, but muscle atrophy is unlikely to be a significant factor.