Time-Series Analysis of Pregnancy and Childbirth Effects on Pelvic Floor Muscle Electrophysiology and Morphology in Rats

INTRODUCTION AND HYPOTHESIS: This study examined the differential effects of pregnancy and parturition on electrophysiological and histomorphometric properties in rat pelvic floor muscle (PFM) groups to provide a theoretical basis for targeted electrical stimulation rehabilitation therapy for specific postpartum PFMs. METHODS: Nine-week-old female Sprague-Dawley rats were divided into control (virgin), pregnancy (15 and 20 days), and postpartum (1 day and 1, 2, and 4 weeks) groups (n = 5 per subgroup). PFM electromyography was recorded through multichannel needle electrodes, and differences in action potentials (APs) and latent periods were analyzed. Hematoxylin-eosin and Masson staining were used to observe muscle fiber morphology and quantify fiber area proportion. RESULTS: Compared with controls, the levator ani AP amplitude was reduced in the 15- and 20-day pregnancy and 1-day postpartum groups (38.49(22.65-106.23), 180.94(49.39-321.41), and 392.07(308.73-443.47) μV vs. 603.91(552.25-708.13) μV; P = 0.014, 0.014, and 0.047, respectively), and latency was significantly prolonged at 1 day postpartum (2.138(2.128-2.175) vs. 2.115(2.089-2.135) ms, P = 0.016); both recovered to baseline by 1 week postpartum. No fluctuations were observed in anal or urethral sphincter parameters (P > 0.05). Compared with controls, the anal sphincter muscle fiber area percentage decreased in the 15- and 20-day pregnancy groups (44.08(26.44-47.74)% and 42.04(32.67-47.47)% vs. 57.60(50.04-65.45)%, P = 0.021 for both) but recovered to baseline at 1 day postpartum. The urethral sphincter muscle fiber area percentage remained stable (P > 0.05). CONCLUSIONS: Pregnancy and parturition affect PFMs differently. The levator ani muscle undergoes reversible electrophysiologic changes, anal sphincter exhibits structural remodeling, and urethral sphincter maintains functional and structural stability.