[Leptin as a marker of sexual dimorphism in newborn infants].

Objective: To determine cord blood leptin levels in newborns appropriate for gestational age, according to gender, birth weight, birth height and ponderal index.

Methods: A cross-sectional study was carried out with 132 term newborns appropriate for gestational age (68 females, 64 males), gestational age between 35-42 weeks. Data were collected through interviews with the mothers at the maternity, anthropometrycal study of the newborns, and cord blood estradiol, testosterone and leptin assays obtained immediately after birth.

Results: The levels of leptin were significantly higher in females than in males (8.34+/-0.65 ng/ml versus 6.06+/-0.71 ng/ml; p = 0.000). The concentrations of estradiol and testosterone did not differ between males and females. Leptin levels were positively correlated with gestational age (r = 0.394, p < 0.01), birth weight (r = 0.466, p < 0.01), birth length (r = 0.335, p < 0.01) and ponderal index (r = 0.326, p < 0.01).

Conclusions: Leptin concentration in the umbilical cord is positively correlated with gestational age, birth weight, birth height, and ponderal index, suggesting its participation in the neonatal growth process. In addition, a gender difference with higher levels of leptin in females neonates was observed, suggesting that the sexual dimorphism in relation to body composition already exists in newborns.