In the adult the concentration of leptin, the OB gene product, correlates closely with the degree of obesity. To clarify whether this relationship is found during fetal development, we measured plasma leptin concentrations in cord blood from 40 term (≥37 wks) newborns with different intrauterine growth pattern. Of the newborns 13 had birth weights appropriate for gestational age (AGA): 3388±409 g (mean±SD), relative weight 0.0±0.7 SD; 15 were large for date (LFD): weight 4125±532 g, relative weight +2.2±1.1 SD; and 12 were small for date (SFD): weight 2376±230 g, relative weight -2.2±0.3 SD. In the AGA group leptin was 12.1±2.7 (mean±SE) μg/l, in LFD 34.2±7.1(p<0.05 vs AGA), and in SFD 3.2±0.5 (p<0.01 vs AGA). A significant correlation was found between birth weight and leptin concentration in cord blood R2=0.32, p<0.001.

Leptin is secreted in the human fetus. A strong correlation exists between body weight and leptin concentration at term. The interaction of fetal leptin with prenatal growth and with postnatal obesity remains to be studied.