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Genetic factors contributing to birth weight
  1. L B Johnston,
  2. A J L Clark,
  3. M O Savage
  1. Department of Endocrinology, St Bartholomew's and the Royal London Schools of Medicine and Dentistry, Queen Mary, University of London, London, UK
  1. Correspondence to:
    Professor Savage, Paediatric Endocrine Section, St Bartholomew's Hospital, West Smithfield, London EC1A 7BE, UK;

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Epidemiological studies suggest that genetic factors account for 30-80% of birth weight variance

The 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 …

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