Fetal leptin influences birth weight in twins with discordant growth

The objective of this study was to determine the plasma leptin concentrations in twin pregnancies in relation to chorionicity and discordant fetal growth. We studied 53 twin pregnancies of which 26 had growth discordance of > or =20% and 27 were concordant for growth (discordance of < or =10%). Paired maternal and fetal blood samples were obtained at birth. Plasma leptin concentrations were measured by RIA. In discordant monochorionic pregnancies, fetal plasma leptin concentrations in the intrauterine growth-restricted twins were lower than the co-twins with normal growth (mean difference, 3 ng/mL; 95% CI, 2.2 to 3.3 ng/mL; p < 0.001), whereas no such differences were present between concordant monochorionic twin pairs (mean difference, 0.1 ng/mL; 95% CI, -0.2 to 0.5 ng/mL; NS). Similarly, fetal plasma leptin concentrations in appropriate-for-gestational-age twins were higher than in the intrauterine growth-restricted twins of the discordant dichorionic pregnancies (mean difference, 2.4 ng/mL; 95% CI, 1.8 to 3.1 ng/mL; p < 0.001). No such differences were present between the concordant dichorionic twin pairs (mean difference, 0.2 ng/mL; 95% CI, -0.1 to 0.5 ng/mL; NS). Maternal plasma leptin concentrations were comparable among all four groups and were higher than the fetal levels. Fetal plasma leptin concentrations of the intrauterine growth-restricted twins of discordant monochorionic and dichorionic pregnancies were comparable. There was a positive association between cord plasma leptin concentrations and the birth weight of twin pairs (y = 0.002x - 0.32; r = 0.63; p < 0.001; n = 106). A significant positive association was also found between percent differences in birth weight and fetal delta plasma leptin concentrations of the discordant monochorionic and dichorionic twin pairs (y = 0.057x + 0.93; r = 0.60; p < 0.001, n = 26). In conclusion, irrespective of chorionicity, plasma leptin concentrations in intrauterine growth-restricted twins were 2-fold lower than their co-twins with normal growth. These differences may be attributed to placental factors.