Maternal insulin resistance in pregnancy is associated with fetal fat deposition: findings from a longitudinal study.

BACKGROUND: Newborns exhibit substantial variation in fat mass accretion over gestation. These individual differences in newborn adiposity extend into infancy and childhood and relate to subsequent risk of obesity and metabolic dysregulation. Maternal glucose homeostasis in pregnancy has been proposed as an underlying mechanism; however, the timing in gestation when maternal glucose regulation influences the progression of fetal fat deposition remain unclear. OBJECTIVE: This study aimed to investigate the cross-sectional and longitudinal association of maternal insulin resistance in early, mid, and late pregnancy with fetal fat deposition in uncomplicated pregnancies. We hypothesized that maternal insulin resistance at early, mid, and late gestation is positively associated with fetal fat deposition, and that the magnitude of the association is greater for the mid and late gestation measures than for the early gestation measure. STUDY DESIGN: In a longitudinal study of 137 low-risk pregnancies, a fasting maternal blood sample was obtained and fetal ultrasonography was performed at ≈ 12, 20, and 30 weeks' gestation. Maternal insulin resistance was quantified using the homeostasis model assessment of insulin resistance (fasting insulin×fasting glucose/405). Estimated fetal adiposity was calculated by integrating measurements of cross-sectional arm and thigh percentage fat area and anterior abdominal wall thickness. The associations between maternal homeostasis model assessment of insulin resistance and estimated fetal adiposity and estimated fetal weight were determined by multiple linear regression adjusted for potential confounding factors including maternal age, parity, race and ethnicity, prepregnancy body mass index, gestational weight gain per week, fetal sex, and gestational age at assessments. RESULTS: Maternal homeostasis model assessment of insulin resistance at ≈ 12, 20, and 30 weeks was 2.79±1.79 (±standard deviation), 2.78±1.54, and 3.76±2.30, respectively. Homeostasis model assessment of insulin resistance at 20 weeks was positively associated with estimated fetal adiposity at 20 weeks (r=0.261; P=.005). Homeostasis model assessment of insulin resistance at 20 weeks (r=0.215; P=.011) and 30 weeks (r=0.285; P=.001) were also positively associated with estimated fetal adiposity at 30 weeks. These relationships remained significant after adjustment for confounding factors. There was no significant correlation between homeostasis model assessment of insulin resistance and estimated fetal weight at 20 and 30 weeks' gestation. CONCLUSION: In low-risk pregnancies, maternal insulin resistance at mid and late but not early pregnancy is significantly associated with fetal adiposity but not with fetal weight. Maternal insulin resistance in mid-gestation could provide a basis for risk identification and interventions that target child adiposity.

Prospective association of fetal liver blood flow at 30 weeks gestation with newborn adiposity.

BACKGROUND: The production of variation in adipose tissue accretion represents a key fetal adaptation to energy substrate availability during gestation. Because umbilical venous blood transports nutrient substrate from the maternal to the fetal compartment and because the fetal liver is the primary organ in which nutrient interconversion occurs, it has been proposed that variations in the relative distribution of umbilical venous blood flow shunting either through ductus venosus or perfusing the fetal liver represents a mechanism underlying this adaptation. OBJECTIVE: The objective of the present study was to determine whether fetal liver blood flow assessed before the period of maximal fetal fat deposition (ie, the third trimester of gestation) is prospectively associated with newborn adiposity. STUDY DESIGN: A prospective study was conducted in a cohort of 62 uncomplicated singleton pregnancies. Fetal ultrasonography was performed at 30 weeks gestation for conventional fetal biometry and characterization of fetal liver blood flow (quantified by subtracting ductus venosus flow from umbilical vein flow). Newborn body fat percentage was quantified by dual energy X-ray absorptiometry imaging at 25.8 ± 3.3 (mean ± standard error of the mean) postnatal days. Multiple regression analysis was used to determine the proportion of variation in newborn body fat percentage explained by fetal liver blood flow. Potential confounding factors included maternal age, parity, prepregnancy body mass index, gestational weight gain, gestational age at birth, infant sex, postnatal age at dual energy X-ray absorptiometry scan, and mode of infant feeding. RESULTS: Newborn body fat percentage was 13.5% ± 2.4% (mean ± standard error of the mean). Fetal liver blood flow at 30 weeks gestation was significantly and positively associated with newborn total fat mass (r=0.397; P<.001) and body fat percentage (r=0.369; P=.004), but not with lean mass (r=0.100; P=.441). After accounting for the effects of covariates, fetal liver blood flow explained 13.5% of the variance in newborn fat mass. The magnitude of this association was pronounced particularly in nonoverweight/nonobese mothers (prepregnancy body mass index, <25 kg/m2; n=36) in whom fetal liver blood flow explained 24.4% of the variation in newborn body fat percentage. CONCLUSION: Fetal liver blood flow at the beginning of the third trimester of gestation is associated positively with newborn adiposity, particularly among nonoverweight/nonobese mothers. This finding supports the role of fetal liver blood flow as a putative fetal adaptation underlying variation in adipose tissue accretion.