Increase of maternal plasma leptin concentrations during pregnancy: comparison with nonpregnant women.

To investigate the physiological changes of leptin levels and whether placenta is linked to its production during pregnancy, plasma of 65 pregnant women at various gestational weeks were compared with those of 34 age- and body mass index (BMI)-matched nonpregnant women in the study. The leptin levels showed a gradual increase from 7-13 gestational week, then continuously elevated during weeks 14-20, 21-27, 28-34, virtually reaching a peak at 35-41 weeks' gestation. When they were compared to those of age- and BMI-matched nonpregnant women, a significant (P < 0.0001) increase was found with every gestational week. There were positive correlations between maternal leptin and BMI of first (7-13th week), second (14-27th week) and third (28-41st week) trimesters, with the correlation coefficients of 0.40 (P < 0.05), 0.54 (P < 0.001), and 0.49 (P < 0.001), respectively. No correlation (r = -0.17, P > 0.05, n = 31) was found between maternal leptin level and the neonatal birth weight. These data suggest that placental production of leptin is one major source of higher levels in maternal circulating leptin other than maternal gain of fat mass and that maternal leptin level is not related to fetal birth weight during pregnancy.