Pelvic floor muscle strength and the incidence of pelvic floor disorders after vaginal and cesarean delivery

BACKGROUND: Pelvic floor disorders (including urinary and anal incontinence and pelvic organ prolapse) are associated with childbirth. Injury to the pelvic floor muscles during vaginal childbirth, such as avulsion of the levator ani muscle, is associated with weaker pelvic floor muscle strength. As weak pelvic floor muscle strength may be a modifiable risk factor for the later development of pelvic floor disorders, it is important to understand how pelvic floor muscle strength affects the course of pelvic floor disorders over time. OBJECTIVE: To investigate the association between pelvic floor muscle strength and the incidence of pelvic floor disorders, and to identify maternal and obstetrical characteristics that modify the association. MATERIALS AND METHODS: This is a longitudinal study investigating pelvic floor disorders after childbirth. Participants were recruited 5e10 years after their first delivery and were assessed for pelvic floor disorders annually for up to 9 years. Stress incontinence, overactive bladder, and anal incontinence were assessed at each annual visit using the Epidemiology of Prolapse and Incontinence Questionnaire. Pelvic organ prolapse was assessed on physical examination, and was defined as descent of the vaginal walls or cervix beyond the hymen during forceful Valsalva. The primary exposure of interest was pelvic floor muscle strength, defined as the peak pressure during a voluntary pelvic muscle contraction (measured with a perineometer). The relationship between pelvic floor muscle strength and the cumulative incidence (time to event) of each pelvic floor disorder was evaluated using lognormal models, stratified by vaginal vs cesarean delivery. The relative hazard for each pelvic floor disorder (among those women free of the disorder at enrollment and thus more than 5e10 years from first delivery), was estimated using semiparametric proportional hazard models as a function of delivery mode, pelvic floor muscle strength, and other covariates. RESULTS: Of 1143 participants, the median age was 40 (interquartile range, 36.6e43.7) years, and 73% were multiparous. On perineometry, women with at least 1 vaginal delivery were more likely to have a low peak pressure, defined as <20 cm H2O (243 of 588 women with at least 1 vaginal delivery vs 107 of 555 women who delivered all of their children by cesarean delivery, P <.001). Among women who had at least 1 vaginal delivery, a pelvic floor muscle strength of <20 cm H2O was associated with a shorter time to event for stress incontinence (time ratio, 0.67; 95% confidence interval, 0.50e0.90), overactive bladder (time ratio, 0.67; 95% confidence interval, 0.51e0.86), and pelvic organ prolapse (time ratio, 0.76; 95% confidence interval, 0.65e0.88). No such association was found among women who delivered all of their children by cesarean delivery. Among women with at least 1 vaginal delivery and considering only pelvic floor disorders that developed during study observation (5e10 years after the first delivery), and controlling for maternal characteristics (body mass index and genital hiatus), women who had a peak pressure of < 20 cm H2O had hazard ratios (relative to similar to 20 cm H2O) of 1.16 (95% confidence interval, 0.74-1.81) for stress incontinence, 1.27 (95% confidence interval, 0.78-2.05) for overactive bladder, and 1.43 (95% confidence interval, 0.99-2.07) for pelvic organ prolapse. Among women who delivered all of their children by cesarean delivery, there was no association between muscle strength and relative hazard of pelvic floor disorders when controlling for maternal characteristics. CONCLUSION: After vaginal delivery, but not cesarean delivery, the cumulative incidence of pelvic organ prolapse, stress incontinence, and overactive bladder is associated with pelvic muscle strength, but the associations attenuate when adjusting for genital hiatus and body mass index.