Paternal contribution to birth weight

Study objective Understanding causes of variation in birth weight has been limited by lack of sufficient sets of data that include paternal birth weig ht. The objective was to estimate risks of low birth weight dependent on pa rental birth weights and to estimate father-mother-offspring correlations f or birth weight to explain the variability in birth weight in terms of effe cts of genes and environmental factors. Design-A family design, using trios of father-mother-firstborn child. Setting-The complete birth population in Norway 1967-98. Participants-67795 families. Main results-The birth weight correlations were 0.226 for mother-child and 0.126 for father-child. The spousal correlation was low, 0.020. The relativ e risk of low birth weight in the first born child was 8.2 if both parents were low birth weight themselves, with both parents being above 4 kg as the reference. The estimate of heritability is about 0.25 for birth weight, un der the assumption that cultural transmission on the paternal side has no e ffect on offspring prenatal growth. Conclusions-Paternal birth weight is a significant and independent predicto r of low birth weight in offspring. The estimate of the heritability of bir th weight in this study is lower than previously estimated from data within one generation in the Norwegian population.