Maternal adipose tissue expansion, a missing link in the prediction of birth weight centile

Context: Maternal body mass index (BMI) is associated with increased birth weight but does not explain all the variance in fetal adiposity. Objective: To assess the contribution of maternal body fat distribution to offspring birth weight and adiposity. Design: Longitudinal study throughout gestation and at delivery. Setting: Women recruited at 12 weeks of gestation and followed up at 26 and 36 weeks. Cord blood was collected at delivery. Patients: Pregnant women (n=45) with BMI 18.0-46.3 kg/m2 and healthy pregnancy outcome. Methods: Maternal first trimester abdominal subcutaneous and visceral adipose tissue thickness (SAT and VAT) was assessed by ultrasound. Results: VAT was the only anthropometric measure independently associated with birth weight centile (r2 adjusted 15.8%, P=0.002). BMI was associated with trimester 2 and trimester 1 – 3 area under the curve (AUC) glucose and insulin resistance (HOMA). SAT alone predicted trimester 2 lipoprotein lipase (LPL) mass (a marker of adipocyte insulin sensitivity) (11.3%, P=0.017). VAT was associated with fetal triglyceride (9.3%, P=0.047). Placental weight was the only independent predictor of fetal adiposity (48%, P<0.001). Maternal trimester 2 and AUC LPL were inversely associated with fetal adiposity (r=-0.69, P=0.001 and r=-0.58, P=0.006 respectively). Conclusions: Maternal VAT provides additional information to BMI for prediction of birth weight. VAT may be a marker of reduced SAT expansion and increased availability of maternal fatty acids for placental transport