Relative and Maximal Intra-abdominal Pressure and Postpartum Pelvic Floor Outcomes in Primiparas Delivered Vaginally

Objectives This study aimed to explore associations between relative and maximal intra-abdominal pressure (IAP) on pelvic floor outcomes in primiparas delivered vaginally. Methods At 5-10 weeks and 1 year postpartum, we measured absolute IAP by vaginal sensor while participants lifted a weighted car seat (IAP(LIFT)) and performed isometric trunk flexion endurance (IAP(TFE)) and seated maximal strain (IAP(STRAIN)). Primary outcomes, completed 1 year postpartum, included worse pelvic floor support (descent to or beyond the hymen) and positive symptom burden (bothersome symptoms in >= 2 of 6 domains on the Epidemiology of Prolapse and Incontinence Questionnaire). We calculated relative IAP (as absolute IAP/IAP(STRAIN)). Results Of 542 participants, 9.7% demonstrated worse support and 54.3% demonstrated symptom burden at 1 year postpartum. In multivariable analyses, absolute IAP(LIFT) and absolute IAP(TFE) at 5-10 weeks postpartum were not associated with worse support. As relative IAP at 5-10 weeks increased, the prevalence of worse support decreased (prevalence ratio [PR] of 0.77 [95% confidence intervals (CIs), 0.63-0.94] and PR of 0.79 [95% CI, 0.67-0.93]) per 10% increase for relative IAP(LIFT) and relative IAP(TFE), respectively. This was largely due to IAP(STRAIN,) which increased the prevalence of worse support (PR, 1.15 [95% CI, 1.06-1.25]) per 10 cm H2O increase. One year postpartum, only IAP(STRAIN) increased the prevalence of worse support (PR, 1.11 [95% CI, 1.02-1.20]) per 10 cm H2O. Of all IAP measures at both time points, only absolute IAP(LIFT) at 1 year significantly increased the prevalence of symptom burden (PR, 1.11 [95% CI, 1.05-1.18]) per 10 cm H2O. Conclusions This exploratory analysis suggests that postpartum IAP(STRAIN) may increase the prevalence of worse support in primiparas delivered vaginally.