Association between infant birthweight and pelvic floor muscle strength: a population-based cohort study

BACKGROUND: To assess the relationship between infant birthweight and pelvic floor muscle (PFM) strength in China. METHODS: We performed a retrospective, single-center cohort study of 1575 women delivering vaginally between January 2017 and May 2020. All participants completed pelvic floor examinations within 5–10 weeks after delivery and were evaluated for PFM strength, which was estimated by vaginal pressure. Data were collected from electronic records. We evaluated the association between infant birthweight and vaginal pressure through multivariable-adjusted linear regression analysis. We also performed subgroup analyses stratified by potential confounders. RESULTS: Vaginal pressure decreased as the quartile of birthweight increased (P for trend < 0.001). Beta coefficients were -5.04 (95%CI -7.98 to -2.1), -5.53 (95%CI -8.5 to -2.57), -6.07 (95%CI -9.08 to -3.07) for birthweight quartile 2–4, respectively (P for trend < 0.001), independent of age, postpartum hemorrhage, and the number of vaginal deliveries. In addition, the results of subgroup analyses showed the same patterns across strata. CONCLUSIONS: This study demonstrates that infant birthweight was associated with decreased vaginal pressure in women after vaginal delivery and could be considered a risk factor for decreased PFM strength in the population with vaginal delivery. This association may provide an extra basis for appropriate fetal weight control during pregnancy, and for earlier pelvic floor rehabilitation of postpartum women delivering babies with larger birthweight.