LEVELS OF LEPTIN IN MATERNAL SERUM, AMNIOTIC-FLUID, AND ARTERIAL AND VENOUS CORD-BLOOD - RELATION TO NEONATAL AND PLACENTAL WEIGHT

The mechanisms by which maternal and fetal weight are regulated during pregnancy are poorly understood. The ob protein, termed leptin, is pr oduced by adipocytes. It is involved in the regulation of body weight by suppressing appetite and stimulating energy expenditure bath in hum ans and rodents. In this study we examined whether leptin concentratio ns in the mother and the newborn correlate with birth weight, placenta l weight, and maternal weight at term. Leptin concentrations were meas ured in amniotic fluid, venous and arterial cord blood, and maternal s erum at birth (n = 27) using a specific RIA employing human recombinan t leptin for tracer and standard preparation. Gestational age was 38-4 2 weeks, maternal age was 21-42 yr, mean maternal weight at birth was 80.0 +/- 10.8 kg, and mean body mass index before pregnancy was 23.4 /- 2.8 kg/m(2). The newborns' mean weight was 3450 +/- 580 g, and mean placental weight was 616 +/- 120 g. Serum leptin levels from nonpregn ant women ranged between 1.7-18.4 ng/mL, median 5.5 ng/ml (n = 30). Me an leptin concentration in maternal serum at birth was 20.0 +/- 13.2 n g/mL and was higher (P < 0.002) than in arterial cord blood (9.7 +/- 9 .4 ng/mL) and venous cord blood (8.9 +/- 8.6 ng/mL). Mean amniotic flu id leptin concentration was 3.6 +/- 2.8 ng/mL. Placental weight correl ated inversely with leptin levels in maternal serum at birth (r = -0.4 9, P < 0.01). In addition, leptin concentrations in venous cord blood correlated significantly with the levels in arterial cord blood (r = 0 .98, P < 0.0001), and leptin levels in cord blood correlated positivel y with birth weight (r = 0.57, P = 0.03] and placental weight (r = 0.5 0, P < 0.01). In contrast, there was no correlation between maternal s erum leptin levels and birth weight. Thus, leptin levels are high in t he fetus and in the mother at term. We hypothesize that high leptin le vels could represent an important feed-back modulator of substrate sup ply and subsequently for adipose tissue status during late gestation.