Differential parental weight and height contributions to offspring birthweight and weight gain in infancy.

BACKGROUND Parental weight and height correlate with offspring birthweight and weight gain, suggesting genetic and environmental influences on fetal growth. The differential contributions of the mother's and father's height and weight to birthweight, or weight gain in infancy, remain unclear and were examined using data from the UK Millennium Cohort Study. METHODS We calculated z-scores for birthweight and conditional weight gain to age 9 months (weight gain adjusted for birthweight) for 6811 term white singleton infants living with natural parents, using the British 1990 growth reference. We also calculated parental height and weight z-scores. The effects of parental size on birthweight and weight gain were analysed using multivariable regression, with a novel reparameterization to test for differences in effect size between mother and father. RESULTS Maternal weight had a far greater influence than paternal weight on birthweight [coefficient for the difference between parents (95% CI): 0.15 (0.100.20)], while parental height contributions were similar [0.03 (-0.02 to 0.07)]. Weights and heights of mothers and fathers contributed equally to infant weight gain [difference coefficients -0.03 (-0.09 to 0.02) and 0.02 (-0.03 to 0.07), respectively]. CONCLUSIONS The influences of parental height and weight on birthweight and infant weight gain are similar for the two parents, with the exception of the influence of weight on birthweight where the mother is much more influential than the father. Parental size associations with infant growth result from a complex combination of genetic and environmental influences. This novel reparameterization of parental anthropometry is applicable to other studies examining parental influences on offspring size and growth across the life course.