Effect of pre-pregnancy obesity and waist-to-hip ratio on pregnancy-related pelvic girdle pain and mode of delivery: a retrospective cohort study

BACKGROUND: Pregnancy-related pelvic girdle pain (PPGP) affects approximately 50% of pregnant women, causing significant disability. While body mass index (BMI) has been associated with PPGP, the role of waist-to-hip ratio (WHR) as a measure of central adiposity remains unclear. This study aimed to investigate the independent and joint effects of pre-pregnancy BMI and WHR on PPGP and cesarean section (CS) risk. METHODS: This retrospective cohort study included 401 women with singleton pregnancies who delivered at term (≥37 weeks) at a tertiary obstetric hospital in Tianjin, China, between January 2020 and December 2024. Pre-pregnancy anthropometric measurements including BMI and WHR were collected at the first antenatal visit (≤12 weeks). PPGP was assessed using a 0-10 numeric rating scale (NRS). Multivariable logistic regression, restricted cubic spline analysis, and predictive modeling were performed using R version 4.3.0. RESULTS: for trend <0.001). Compared to normal weight women, obese women had increased risk of PPGP (adjusted OR [aOR] 2.24, 95% CI 1.29-3.89) and CS (aOR = 2.36, 95% CI 1.36-4.10). Elevated WHR (≥0.85) was independently associated with PPGP (aOR 1.89, 95% CI 1.28-2.79) and CS (aOR = 1.72, 95% CI 1.18-2.51). Women with both overweight/obese BMI and elevated WHR had the highest risk (PPGP: aOR = 2.56; CS: aOR = 2.68; P for interaction: 0.042 and 0.068, respectively). The combined BMI-WHR model demonstrated excellent predictive performance (AUC: 0.856 for PPGP, 0.842 for CS). CONCLUSIONS: Pre-pregnancy obesity assessed by both BMI and WHR independently increases the risk of PPGP and CS, with synergistic effects when combined. WHR provides additional predictive value beyond BMI alone. Pre-pregnancy weight management targeting both general and central adiposity may help reduce these adverse outcomes.