Associations between physical activity, sedentary behavior, body mass index and changes in placental structure and vascularization – data from the FitMum randomized controlled trial

OBJECTIVE: Maternal physical activity (PA), sedentary time (ST) and body-mass index (BMI) might influence placental development. We examined associations between PA, ST during pregnancy and pre-pregnancy BMI, and placental structural outcomes as well as mRNA expression levels of vascular growth factors. METHODS: The FitMum randomized controlled trial included 220 healthy, pregnant women. PA and ST were objectively measured 24/7 from inclusion before gestational week 15 + 0 until delivery. This secondary analysis of FitMum includes all participants with an available placenta sample (n = 118). Placental sections were stained with immunofluorescence and H&E. Villous density as well as vessel area were assessed with Visiopharm software. Placental samples with sufficient quality (n = 107) were bulk RNA-sequenced and genes relevant for placental vascularization were selected for analysis. Associations of moderate-to-vigorous intensity PA (MVPA), ST and pre-pregnancy BMI, with villous density, vessel surface area, placental weight, and mRNA-counts, were analyzed with multiple regressions. RESULTS: Increased MVPA was associated with increased placental weight (p = 0.005), while higher pre-pregnancy BMI was associated with lower area of medium-sized and large blood vessels in the placenta (p = 0.002). No associations were observed between MVPA or ST and histologic outcomes or mRNA expression levels. CONCLUSION: PA during pregnancy was not associated with vessel per villous area or villous density nor mRNA expression levels of vascular growth factors, but with increased placental weight. High pre-pregnancy BMI was associated with lower area of medium-sized and large blood vessels in the placenta, suggesting metabolic status before pregnancy may play a key role in placental vascular development.