Leptin concentration in newborns' cord blood: relationship to gender and growth-regulating hormones

To verify if plasma leptin concentrations of newborns at birth differ significantly between sexes; and to investigate the potential interactions between plasma leptin and growth-regulating hormones at birth.

98 healthy newborns (48 male, 50 female) were studied. Leptin, insulin, cortisol, insulin-like growth factor-1 (IGF-1), testosterone, and sex hormone binding globulin (SHBG) concentrations were measured from venous blood collected from the umbilical cord vein immediately after birth.

The serum leptin concentration of newborns averaged 8.05(0.5) ng/ml. Females had significantly (P<0.005) higher serum leptin values than males [9. 6(0.8) vs 6.0(0.6) ng/ml]. IGF-1 was significantly (P<0.05) higher in females than in males [87(4) vs 74(5) microg/l], whereas SHBG was slightly lower [29(1) vs 33(2) nmol/l]. Insulin, cortisol, and testosterone serum concentrations were not statistically different between the sexes. Among the variables examined, birth weight (expressed as Z-score of weight) and insulin showed the highest degree of relationship with serum leptin in newborns (r=0.48 and r=0.31 respectively, P<0.001). Multiple regression analysis showed that Z-score of birth weight, gender and cortisol were able to account for approximately 44% of inter-individual variability of serum leptin concentrations in newborns.

Female newborns have significantly higher serum leptin concentrations than males. Insulin, IGF-1, testosterone, and SHBG did not independently affect leptin inter-individual variability when gender, Z-score of body weight, and cortisol were taken into account. Other factors may be involved in the differences in circulating leptin concentrations between the sexes in newborns.