Background: Leptin is produced by adipose tissue, and the protein plays a role in regulation of food intake and metabolism. Plasma concentration of the hormone is correlated to body fat mass, and gender differences have been reported both in adults and children.

Subjects: 180 pregnant women and their newborn infants.

Interventions: P-leptin concentration was measured by radio-immunoassay during pregnancy in week 18 and 35, in the umbilical cord, and at 4 and 13 weeks of age.

Results: Maternal P-leptin increased from 15.5±9.0 μg/L(n=175) in week 18 to 17.7±10.7 μg/L (n=166) (p=0.01, n=163) in week 35. During the same time period, the body mass index (BMI) increased from 24.2±3.3 kg/m2 to 27.8±3.3 kg/m2 (p<0.001, n=174). Gender difference in P-leptin concentration was present already at birth in umbilical cord (10.8±9.2 μ/L for girls (n=65) vs. 7.6±6.6 μg/L for boys (n=74) (p=0.01)). A gender difference in P-leptin concentration was also found at four weeks (3.9±1.8 μg/L, n=68 vs. 3.2±1.8 μg/L, n=71) (p=0.003) and 13 weeks (4.9±2.1μg/L, n=61 vs. 4.1±3.1 μ/L, n=73) (p=0.006). P-leptin in umbilical cord correlated with birth weight (r=0.44, p<0.001, n=124) between P-leptin and weight at 13 weeks of age.

Conclusion: The maternal P-leptin levels increased during pregnancy and correlated to BMI. Our findings demonstrate for the first time that gender differences in P-leptin concentrations are present already at birth. A reduction to 39% in P-leptin concentration was found from birth to four weeks of age. There was significant correlation between body weight and P-leptin levels both at birth and at 13 weeks of age.