The role of maternal weight, body composition, systemic inflammation, and mental health in the onset and persistence of pregnancy-related lumbopelvic pain: A study protocol

Abstract

Introduction: Pregnancy-related lumbopelvic pain (PLPP) affects 50 to 90% of pregnant women. While higher maternal body weight and excessive gestational weight gain have been recognized as risk factors for PLPP, prior studies did not differentiate between fat and fat-free mass. At the same time, higher fat mass is known to be associated with low back pain in non-pregnant populations, potentially through adiposity-related systemic inflammation. This inflammation is linked to depression and anxiety, known risk factors for PLPP. However, the longitudinal interplay of maternal body weight, fat mass, inflammation, and psychological factors influencing PLPP remains unexplored.

Purpose/Aim: This study aims to (1) determine whether maternal body weight or fat mass predicts PLPP onset and persistence, and (2) examine the mediating and moderating roles of depression, anxiety, and systemic inflammation.

Materials and Methods: This longitudinal cohort is part of the PROFit study (G0A1N24FWO/NCT06785909). We will recruit 211 pregnant women without PLPP in the first trimester and follow them up in the third trimester, and six weeks and nine months postpartum. PLPP will be assessed using clinical tests, pain intensity evaluations (Visual Analogue Scale), and disability (modified Oswestry Disability Index). Body weight and height will be recorded, and fat mass will be measured using bioelectrical impedance analysis. Inflammatory blood variables will be assessed biochemically, and psychological factors with validated questionnaires. Data will be analyzed using group comparisons, regression models, latent class growth analysis, and cross-lagged panel modelling.

Results: By December 2025, 31 participants (age: 31.3±3.6 years; BMI: 24.9±4.2 kg/m², body weight: 68.8±12.7 kg, fat percentage: 32.5±6.7%) were included and tested in the first trimester. Eight of them were assessed in the third trimester, of whom four reported PLPP (pain intensity ranging 15-70/100, disability ranging 6-24/100). Women with PLPP had a Δ BMI of +2.9kg/m², a Δ body weight of +7.9kg compared to the first trimester, and a fat percentage of 34.0±7%. The women without PLPP had a ΔBMI of +3.7kg/m², a Δ body weight of +9.9kg compared to the first trimester, and a fat percentage of 31.1±2.6%. Given the small sample size, group comparisons were not performed.

Conclusion: This study will provide novel longitudinal insights into the interplay between maternal weight, body composition, inflammation, and mental health in the onset and persistence of PLPP, guiding the improvement of prevention and intervention strategies.