Sex differences in the association of cord blood insulin with subcutaneous adipose tissue in neonates

BACKGROUND: Excessive fat accumulation characterizes the over-nourished fetus in maternal diabetes and obesity with fetal insulin regarded as a primary driver. This study tested whether fetal insulin is related to subcutaneous adipose tissue (SAT) thickness at different body sites in neonates, and whether sites respond differentially to insulin. In addition, sex differences were assessed. METHODS: Cord blood insulin was measured for 414 neonates. After birth, SAT thickness was measured at 15 body sites using a validated device, a lipometer, that measures back-scattered light intensities corresponding to SAT. Associations between fetal insulin and SAT were assessed in linear regression models, adjusted for gestational age and birth weight, for males and females separately. RESULTS: No sex differences in insulin levels or total SAT thickness were found. In males, SAT thickness at most body sites was significantly correlated with insulin, with strongest associations between insulin and SAT on neck (beta 0.23, 95% CI 0.05; 0.41; P = 0.01) and upper abdomen (beta 0.18, 95% CI 0.01; 0.36; P = 0.04). In females, insulin was only associated with hip SAT thickness (beta 0.22, 95% CI 0.06; 0.39; P = 0.01). Total SAT thickness was correlated with insulin in males (beta 0.03, 95% CI 0.01; 0.04; P = 0.003), but not in females (beta 0.01, 95% CI - 0.01; 0.02; P = 0.38). CONCLUSIONS: Fat deposition in female neonates seems less affected by insulin as compared to males. This may reflect lower insulin sensitivity in females, or may be accounted for by other metabolic/endocrine factors overriding the association.