Pelvic floor dysfunction and weakening of the pelvic floor muscles (PFMs) during vaginal delivery play a major role in postpartum incontinence. It is believed that vaginal childbirth may result in reduced vaginal resting pressure (VRP) and reduced PFM strength and endurance, whereas cesarean section (CS) may protect the PFM. Several studies have assessed change in PFM strength from pregnancy to shortly after childbirth in relation to mode of delivery; the results were conflicting. Moreover, most such studies were small, few were prospective, and none addressed change in VRP when comparing modes of delivery.
This prospective cohort study was designed to investigate the impact of delivery mode on VRP and PFM strength and endurance and to determine whether measurements of VRP and PFM differed in women with and without urinary incontinence. A total of 277 nulliparous women were followed from midpregnancy to 6 weeks postpartum. Changes from midpregnancy to 6 weeks postpartum were analyzed using a manometer. Differences within groups were assessed by t test; differences between groups were assessed by analysis of variance.
Within the emergency cesarean group, the only significant change was found in VRP (10% reduction, P = 0.001). Compared with the CS group, VRP in the normal and instrumental vaginal delivery groups was reduced by 29% and 30%, respectively, whereas PFM strength was reduced by 54% and 66% and PFM endurance by 53% and 65%, respectively. When comparing CS with normal and instrumental vaginal delivery, significant differences were found for all PFM measures (P < 0.001 for both comparisons). Compared with incontinent women, continent women at both midpregnancy and at 6 weeks postpartum had significantly higher PFM strength and endurance (P < 0.05 for both).
These findings show that vaginal delivery is associated with significant reductions in VRP and in PFM strength and endurance. The data indicate that continent women are stronger than their incontinent counterparts after vaginal delivery and can cope better with the substantial decline in PFM strength and endurance.