Maternal nutrition as a determinant of birth weight.

hat factors determine birth weight and do they have any biological significance for the future health and welfare of the individual? These are important questions for all paediatricians and four groups of experts have been approached to independently give their thoughts on key areas. The aim was for concise pithy comments and opinions, so the length of the articles was rigourously controlled. Firstly, are there genetic factors that contribute to birth weight, secondly does maternal nutrition determine size, then are there social influences on birth weight? Is birth weight of biological significance for the individual or the spe-cies? Patrick Cartlidge, Senior Lecturer in child health in Cardiff, kindly refereed this symposium. Please feedback your views and comments to the rapid response section of the journal website at T he genetic influence on birth size has been recognised for many years, but only recently have some of the specific genes and chromosomal loci involved been identified. This article outlines the evidence for a genetic influence on birth size and reviews our current understanding of the specific genetic factors involved. Epidemiological studies estimate that environmental influences account for about 25% birth weight variance and genetic influences account for 38–80% birth weight variance. 1–3 There is considerable variability in the estimates of the fetal and parental components of these genetic influences from 18 to 69.4% and from 3 to 20% variance of birth weight respectively. Overall there is strong evidence that genetic factors play a significant role in determining birth size. " Thus there is evidence of strong familial trends in birth size. " Familial trends in birth weight have also been observed. There is significant correlation between parental birth weights and birth weight in index cases using multiple regression analysis (mothers 0.19–0.20; fathers 0.12–0.16). 4 5 Maternal and paternal birth weights were significantly lower in families with two small for gestational age (SGA) births (index child below 10th centile) compared with families with no SGA births in the Scandinavian SGA study. 5 The odds ratio calculated for having an SGA mother and SGA father in families with two SGA births were 1.74 and 2.49. A mother born SGA is 2.5 (white) or 2.7 (African American) times more likely to have an SGA child than a mother of normal birth weight, and this increased to 10.2 and 10.1 if there was also a low birthweight sibling. 6 A study of cousins in which …