Levator ani abnormality 6 weeks after delivery persists at 6 months.

Objective: Assess postpartum changes in the levator ani muscle using magnetic resonance imaging and relate these changes to obstetric events and risk factors associated with pelvic floor dysfunction.

Study Design: A board-certified radiologist specializing in abdominal imaging evaluated 146 pelvic magnetic resonance studies from 57 primiparous women 6 weeks and 6 months after first obstetric delivery and 32 nulliparous women. A yes/no determination of muscle body and insertion integrity, muscle thinning, and measurement of muscle thickness in millimeters was made for each of 4 muscle sites: right and left puborectalis and right and left ileococcygeous. Incidence of muscle abnormality and mean muscle thickness was tested in pairs between (1) nulliparous women and 6-week primiparous women; (2) 6 week and 6 month primiparous pairs; and (3) 3 age/race groups using test of 2 proportions and 1-way analysis of variance.

Results: Initial review indicated only 3 subjects not of African American or white race, and only 1 African American primiparous woman of age 30 years or older; therefore, statistical analysis was limited to 45 primiparous women and 25 nulliparous women. Incidence of any abnormality at any of the 4 sites was considered abnormal. In those subjects recovering to normal magnetic resonance by 6 months, an average of nearly 60% increase in right puborectalis muscle thickness compared with that seen at 6 weeks indicated the extent of the injury. Subjects with injury to both the puborectalis and ileococcygeous at 6 weeks did not recover to normal at 6 months, whereas those with injury only to the puborectalis tended to have normal magnetic resonance images at 6 months.

Conclusion: Nulliparity did not guarantee a normal assessment of levator ani anatomy by our blinded reader, and frequency of injury in this series is somewhat greater than that previously reported for primiparous women. Younger white primiparous women had a better recovery at 6 months than older white women. Subjects experiencing more global injury, in particular to the ileococcygeous, tended not to recover muscle bulk.