Umbilical cord blood samples were collected from 12,804 consecutive deliveries, and cord plasma samples were collected from 585 singleton infants born in Norway at term after uncomplicated pregnancies.  These were analyzed for plasma leptin, IGF-I, IGFBP-1 and IGFBP-3.  Data were analyzed following log transformation of IGFBP-1 and leptin values.   Linear regression analysis was used to determine the contribution of maternal and infant factors to umbilical levels of these hormones.  The mean age of the mothers of these infants was 28 years.  Seven percent had smoked at the beginning of the pregnancy, and 36 percent were primiparous.  Male infants had a higher birth weight and length than girls, but girls had a higher ponderal index.  Leptin and IGF-I levels were higher in the cord blood of female infants than in males. None of the maternal factors which were analyzed, including pre-pregnancy weights, smoking, or number of previous pregnancies were significantly associated with levels of cord leptin. IGF-I, IGFBP-3, and leptin increased proportionately with increasing birth weight.  Levels of IGF-I and leptin were the strongest predictors of both birth weight and birth length, and were independent of length of gestation, maternal age, parity, pre-pregnancy weight, smoking and offspring sex. 

The authors conclude that their data suggest that the sexual dimorphism in the regulation of leptin and IGF concentrations, which previously was demonstrated in later childhood, may already be established at birth.  They also suggest a possible role for leptin and/or the IGF–I system in relation to birth size and to the risk of diseases such as non-insulin dependent diabetes and cardiovascular disease which have been shown to be frequent in low birth weight infants.

Editor’s Comment:  These findings have important implications for understanding the relationship between low birth weight and adult morbidity - especially cardiovascular disease, hypertension, and type 2 diabetes. It would appear that leptin, IGF-I, and IGFBP-I, which have been shown to be important factors in growth in utero, may be important in understanding the risk of developing these adult diseases.  It would be very important to follow a cohort of children from birth through adulthood with serial measurements of IGF-I, IGFBP-3, and leptin in order to better understand how these factors change over time and how they might contribute to the development of serious adult disorders. Studies such as those by Vatten et al in Norway support the importance of conducting such difficult epidemiological studies.

William L. Clarke, MD