Fetal leptin and insulin levels only correlate in large-for-gestational age infants

Objective: To determine whether fetal leptin levels correlate with fetal we ight and whether such correlation is direct or indirect via insulin or huma n placental lactogen (hPL), respectively. Design: Cross-sectional study of offspring at term (n = 175) with over-repr esentation of large-for-gestational age (LGA; n = 70) and small-for-gestati onal age (SGA: n = 23) cases in a population of Caucasian women with no pre gnancy pathology. Methods: Fetal cord blood was collected after delivery. In several cases (n = 62) paired mother-fetus blood samples were obtained. Leptin, insulin and hPL levels were measured by RIA. Anthropometric data (birth weight, body m ass index, placental weight) were recorded. Results and Conclusions: Maternal insulin, hPL and leptin levels were highe r than fetal concentrations. Cord blood leptin levels positively correlated with the anthropometric data with stronger correlations in female (0.54 < r < 0.66) than in male (0.32 < r < 0.39) neonates, Cord blood leptin levels did not differ between appropriate-for-gestational age (AGA; n = 82) and S GA (n = 23) neonates, but were higher (P < 0.001) by 83% in LGA (n = 70) th an in AGA neonates, Among the different weight classes the correlations bet ween fetal leptin and anthropometric data were only observed in LGAs, but n ot in AGAs or SGAs, Fetal, but not maternal, leptin levels strongly correla ted with fetal insulin (r = 0.56; P < 0.001). After accounting for this clo se relationship insulin could no longer be used to predict birth weight (r = 0.15, P = 0.051), We suggest that the correlation of cord blood insulin with neonatal weight in LGAs is, in addition to insulin's direct anabolic action, indirectly med iated via leptin. It is hypothesized that fetal insulin stimulates fetal ad ipocyte leptin production.