Lactation is Associated with Accelerated Postpartum Pelvic Floor Muscle Recovery in a Pregnant Simulated Birth Injury Model

Healthy pelvic floor muscles (PFMs) are essential for proper pelvic floor function. The biggest risk factor for PFM dysfunction is injury sustained during vaginal childbirth, yet the factors that facilitate or impair PFM recovery from birth injury remain unknown. We aimed to assess the impact of the postpartum milieu in the presence and absence of lactation on PFM regeneration following simulated birth injury (SBI) in a pregnant rat model. We determined that lactating rats have a rapid increase in systemic immune markers in response to SBI, which contributes to rapid changes in PFM immune cell infiltration and decrease in pro-inflammatory genes. PFMs in lactating rats have enrichment of anti-inflammatory genes and larger newly formed myofibers that contribute to larger myofiber size after weaning. This suggests that lactation promotes an earlier anti-inflammatory response in injured PFMs that allows for quicker myogenesis and myofiber hypertrophy.