Mid-pregnancy maternal leptin levels, birthweight for gestational age and preterm delivery.

OBJECTIVE: Maternal blood leptin levels are positively associated with adiposity. Recent studies suggest that leptin is also abundantly produced by the placenta and may function as a regulator of foetal growth. Our goal was to examine mid-pregnancy levels of leptin in maternal blood in relation to birthweight for gestational age (BW/GA) and timing of delivery after accounting for maternal prepregnancy body mass index (prepreg-BMI) and pregnancy complications. PATIENTS: Data were from 1304 subcohort mother/infant pairs who participated in the Pregnancy Outcomes and Community Health (POUCH) Study (1998-2004). MEASUREMENTS: Leptin levels, measured at 16-27 weeks' gestation, were log-transformed. Geometric mean (GMean) leptin levels were estimated by weighted linear regression with gestational age at blood draw as a covariate. GMean was re-transformed to the original scale for reporting.
RESULTS: Using the GMeans leptin in mothers of term appropriate-for-gestational age (AGA) neonates as the referent (25·2 μg/l), we observed lower levels in mothers of preterm-AGA (21·9 μg/l), term small-for-gestational age (SGA) (20·3 μg/l) and preterm-SGA neonates (21·7 μg/l). Results were largely unchanged after adjustment for prepreg-BMI. Leptin levels were higher in mothers who delivered large-for-gestational age (LGA) neonates, both preterm (33·6 μg/l) and term (29·1 μg/l), but the GMeans were markedly attenuated after adjustment for prepreg-BMI.
CONCLUSION: The association between BW/GA and maternal leptin levels after adjustment for prepreg-BMI may represent: (i) a residual effect of maternal adiposity that is not fully captured by BMI; and/or (ii) variation in placental leptin levels entering the maternal circulation. In conclusion, mid-pregnancy maternal blood leptin levels may be an early indicator of foetal growth status.