How well can pelvic floor muscles with major defects contract? A cross-sectional comparative study 6 weeks after delivery using transperineal 3D/4D ultrasound and manometer

Objective: To investigate ability to contract, vaginal resting pressure (VRP), pelvic floor muscle (PFM) strength and PFM endurance 6 weeks after vaginal delivery in primiparous women, with and without major defects of the levator ani (LA) muscle.

Design: Cross-sectional comparative study.

Setting: Akershus University Hospital, Norway.

Sample: A cohort of 175 singleton primiparous women delivering vaginally after more than 32 weeks of gestation.

Methods: Major LA defects were assessed by 3D/4D transperineal ultrasound at maximal PFM contraction, using tomographic imaging. VRP, PFM strength and PFM endurance were measured vaginally by manometer. Data were analysed by independent-samples Student's t test, chi-square test, and standard multiple and simple linear regression.

Main outcome measures: VRP, PFM strength and PFM endurance.

Results: Of the women included in the study, 4% were not able to contract their PFM 6 weeks after delivery. Women with major LA defects (n = 55) had 47% lower PFM strength and 47% lower endurance when compared with women without major LA defects (n = 120). Mean differences were 7.5 cmH2O (95% CI 5.1-9.9, P < 0.001) and 51.2 cmH2O seconds (95% CI 32.8-69.6, P < 0.001), respectively. These estimates were unchanged by adjustment in multivariable linear regression for potentially confounding demographic and obstetric factors. No difference was found regarding VRP (P = 0.670).

Conclusions: Women with major LA defects after vaginal delivery had pronounced lower PFM strength and endurance than women without such defects; however, most women with major LA defects were able to contract the PFM. This indicates a potential capacity by non-injured muscle fibres to compensate for loss in muscle strength, even at an early stage after delivery.