Structural changes in puborectalis muscle after vaginal delivery

Objective: To evaluate the structural composition of the puborectalis muscle before and at several timepoints after first vaginal delivery, by the use of echogenicity and area measurements, in order to explore its recovery. Methods: Twenty nulliparous women with a singleton pregnancy underwent 3D/4D transperineal ultrasound assessments at rest, on pelvic floor muscle contraction and on Valsalva maneuver at 12 weeks' gestation and at 1 day and 1, 2, 3, 4, 6, 12, 18 and 24 weeks after vaginal delivery. The puborectalis muscle was delineated for measurements of mean echogenicity (MEP) and area (PMA). To assess changes in MEP and PMA over time, linear mixed model analysis was used. The exact number of days after delivery at each ultrasound examination was used as a covariate. Results: For all timepoints after delivery, MEP was significantly decreased compared with that at 12 weeks' gestation. MEP values increased significantly over time from 1 day to 24 weeks after delivery. Although not statistically significant, a decrease in MEP was observed between 3 and 4 weeks after delivery for all maneuvers. PMA at rest and on Valsalva maneuver remained constant after delivery. Conclusion: When compared with measurements taken during pregnancy, a sharp decrease in MEP was observed soon after vaginal delivery, which was most likely caused by stretch trauma to the puborectalis muscle and subsequent formation of (micro) hematoma and edema. Subsequent increases in MEP may reflect the disappearance of hematoma and edema, and also the formation of connective and scar tissue.