Maternal and umbilical cord serum leptin concentrations in small-for-gestational-age and in appropriate-for-gestational-age neonates: a maternal, fetal, or placental contribution?

Leptin is secreted during pregnancy by the placenta and by the maternal and fetal adipose tissues. The leptin levels mainly reflect the amount of fat stored and thus are indicative of the energy balance, i.e., small-for-gestational-age (SGA) neonates represent the negative metabolic balance of in utero starved babies. We chose to compare maternal and umbilical cord leptin levels in pregnancies complicated by asymmetrical SGA versus those with appropriate-for-gestational-age (AGA) neonates as well as a model of multifetal growth concordant gestations in order to establish through the 'leptin link' the relative contributions of mother, fetus, and placenta to fetal weight. We found that the maternal leptin levels at delivery correlated poorly with the maternal weight gain/body mass index and with neonatal birth weight. Furthermore, the umbilical cord leptin levels correlated well with neonatal and placental weights in the AGA group but not in the SGA group. As in AGA singleton pregnancies, in multifetal uncomplicated pregnancies, the umbilical cord leptin levels correlated well with the birth weight of individuals, regardless of the status of the twin or triplet in the set. Thus, we speculated that in SGA neonates the birth weight represents the lean body weight and the low adipose tissue content (as opposed to the AGA neonates who have a substantial adipose tissue content) and, therefore, reflects mainly the basic placental contribution.