(356) Changes in maternal body composition parameters across gestation vary by prepregnancy BMI

Obesity and excessive gestational weight gain are established risk-factors for multiple adverse perinatal complications, but the pathophysiology underlying these risks is poorly understood. We sought to evaluate whether the pattern of weight gain and potential changes in body composition throughout pregnancy varies by pre-pregnancy BMI.


Study Design:

Primary analysis of a prospective cohort. Pregnant individuals at high risk for medically-indicated or spontaneous PTB were recruited from a single MFM outpatient clinic, 2021-2023. Direct segmental multi-frequency bioelectrical impedance analysis technology was used to measure each participant’s body composition up to 4 times during pregnancy using the non-invasive InBody 270 scale-type device. Participants were grouped by pre-pregnancy BMI category (normal < 25, overweight 25-29.9, obese 30-39.9, morbidly obese ≥ 40 kg/m2) and body composition parameters were compared. Data were analyzed by fixed-effects linear regression accounting for varying numbers of observations per subject.

 

Results:

284 InBody assessments were obtained from 153 subjects (24% normal weight, 22% overweight, 33% obese, and 21% morbidly obese). The population was racially (36% Black) and ethnically (20% Latinx) diverse. Initial InBody assessments occurred at a median 19.0 (IQR 15.4-24.7) weeks’; most (57%) were obtained between 14-28 weeks’. Body weight and composition varied significantly across gestation and by BMI category (Figure). Patients with normal BMIs had increased % fat as pregnancy progressed, but had reduced % skeletal muscle mass and % total body water (p< 0.001). In contrast, those with morbid obesity had increased % total body water and % skeletal mass, accompanied by reductions in % body fat as pregnancy progressed (p< 0.001).


Conclusion: Pregnancy is associated with distinct shifts in body composition that vary by pre-pregnancy BMI among individuals at high-risk for adverse pregnancy outcomes. An improved understanding of how pregnancy physiology differs by BMI may provide key insight into obesity-mediated disease associations and morbidities.