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

AIMS: 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.

SUBJECTS: 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.

RESULTS

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.

CONCLUSIONS

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.