The aim of this study was to evaluate leptin concentration at birth and in early postnatal life in small- and appropriate-for-gestational-age infants and to assess its relationship with infants' anthropometry at birth and some characteristics of maternal pregnancy.
Materials and methods: A total of 367 infants born after 32-42 weeks of gestation were enrolled in the study. Umbilical cord blood samples were collected from 80 small- and 287 appropriate-for-gestational-age newborns. Altogether, 166 venous blood samples were taken from these neonates on days 2-6 of life.
Results: Cord leptin levels were significantly lower in small- compared to appropriate-for-gestational-age infants. We observed a positive correlation between cord leptin and birth weight, all neonatal anthropometric parameters, placental weight, and some maternal nutritional factors. In multivariate analysis, cord leptin concentration explained up to 15% of the variation in sum of newborn's skinfold thickness but only 5% of the variation in birth weight. Postnatally, leptin concentration decreased markedly to the similar low levels in both infant groups and remained so during the first postnatal week.
Conclusions: Significantly lower cord leptin concentration in small-for-gestational-age neonates reflects a lower fat mass content compared to appropriate-for-gestational-age infants. However, an abrupt decrease in leptin levels shortly after birth in both groups suggests that placenta could be an important source of leptin in fetal circulation. The impact of low leptin levels at birth in small-for-gestational-age infants on their postnatal appetite and weight gain remains to be elucidated in future studies.