Risk factors for persistent postpartum low back and pelvic pain: a prospective cohort study focusing on trunk muscle...

Persistent low back and pelvic pain (pp-LBPP) is a common postpartum condition with important implications for maternal function and quality of life. However, its underlying mechanisms remain insufficiently understood. While reduced trunk muscle mass (TMM) has been associated with chronic low back pain in nonpregnant populations, its relevance in the postpartum period, characterized by unique physiological and biomechanical changes, has not been prospectively evaluated, highlighting a critical knowledge gap in postpartum musculoskeletal health. This study aimed to examine the association between early postpartum TMM and pp-LBPP and to identify independent risk factors.

This prospective observational study enrolled pregnant women with LBPP at 35 weeks' gestation. TMM was measured at four weeks postpartum using bioelectrical impedance analysis and indexed by height (TMM-I, kg/m²). Persistent pain was assessed at four months postpartum. Multivariable logistic regression analyses were performed to evaluate associations between pp-LBPP and maternal, obstetric, and behavioral variables.

Among 209 participants, 48% reported pp-LBPP at four months postpartum. Multivariate analysis identified older maternal age (aOR 1.10; 95% CI 1.03-1.18), primiparity (aOR 2.53; 95% CI 1.27-5.02), cesarean delivery (aOR 3.29; 95% CI 1.49-7.26), and lack of pre-pregnancy athletic activity (aOR 2.03; 95% CI 1.02-4.01) as independent risk factors. TMM-I was not significantly associated with pp-LBPP.

In this prospective postpartum cohort, early postpartum TMM was not independently associated with persistent pain, suggesting that muscle quantity alone may not explain pain persistence after childbirth. Instead, obstetric and modifiable behavioral factors were significant contributors. These findings highlight the importance of preventive strategies, including pre-pregnancy physical activity and targeted postpartum care, in this understudied population, shifting the focus from muscle quantity to modifiable clinical and behavioral determinants.