Prospective Randomized Trial of Cesarean Delivery versus Vaginal Delivery for Effects on the Pelvic Floor in Squirrel Monkeys

Abstract

Objectives: Vaginal delivery is a risk factor in pelvic floor disorders. We previously described changes in the pelvic floor associated with pregnancy and parturition in the squirrel monkey, a species with a humanlike pattern of spontaneous age and parity associated pelvic organ prolapse. The potential to prevent or diminish these changes with scheduled cesarean section has not been evaluated in a randomized, controlled trial. Therefore, this trial compares female squirrel monkeys undergoing spontaneous vaginal delivery with those undergoing scheduled primary cesarean section for pelvic floor muscle volumes, muscle contrast changes, and dynamic effects on bladder neck position. Materials and Methods: In a prospective randomized trial Levator ani (LA), obturator internus (OI), and coccygeus (COC) muscle volumes and contrast uptake were assessed by MR imaging in 20 nulliparous females examined prior to pregnancy, a few days after delivery, and 3 months post-partum. The position of bladder neck relative to boney reference line was also assessed with abdominal pressure using a dynamic MRI. Results: Baseline measurements of 10 females randomly assigned to scheduled primary cesarean sections were not different from those of 10 females assigned to spontaneous vaginal delivery. LA and OI muscle volume did not differ between the two groups. However, the volume was reduced (p 0.05) in the observation immediately after pregnancy for both muscles. The COC muscles increased (p 0.05) immediately after delivery for females in the spontaneous vaginal delivery group, but did not change in females in the scheduled cesarean section group. Position of the bladder neck descended (p\0.05) by 3 months post-partum in both groups. Conclusion: This study provides the first observations in a randomized, controlled trial that scheduled cesarean section diminishes changes in COC muscle volume and contrast reported to be associated with spontaneous vaginal delivery. However, pelvic support of the bladder was not protected by this intervention suggesting that effects of pregnancy and delivery are not uniformly prevented by this procedure.