Genetic and Environmental Influences on Birth Weight, Birth Length, Head Circumference, and Gestational Age by Use of Population-based Parent-Offspring Data

TLDR

Familial correlations in birth weight and gestational age are largely attributable to fetal and maternal genetic factors, as shown in twin studies. This study aimed to quantify and compare fetal and maternal genetic effects and shared sibling environmental influences on birth weight, gestational age, crown‑heel length, and head circumference. Using path analysis and maximum likelihood on 101,748 parent‑offspring families from the Norwegian Medical Birth Registry (1967‑2004), the authors estimated these effects while adjusting for covariates. They found fetal genetics accounted for 31 % of birth weight and length variation, 27 % of head circumference, and 11 % of gestational age, whereas maternal genetics explained 22 %, 19 %, and 14 % respectively, with fetal genes being most influential for length and head circumference.

Abstract

Familial correlations in birth weight and gestational age have been explained by fetal and maternal genetic factors, mainly in studies on offspring of twins. The aim of the present intergenerational study was to estimate and compare fetal and maternal genetic effects and shared sibling environmental effects on birth weight and gestational age and also on crown-heel length and head circumference. The authors used path analysis and maximum likelihood principles to estimate these effects and, at the same time, to adjust for covariates. Parent-offspring data were obtained from the Medical Birth Registry of Norway from 1967 to 2004. For the analysis of birth weight and crown-heel length, 101,748 families were included; for gestational age, 91,617 families; and for head circumference, 77,044 families. Assuming no cultural transmission and random mating, the authors found that fetal genetic factors explained 31% of the normal variation in birth weight and birth length, 27% of the variation in head circumference, and 11% of the variation in gestational age. Maternal genetic factors explained 22% of the variation in birth weight, 19% of the variation in birth length and head circumference, and 14% of the variation in gestational age. Relative to the proportion of explained variation, fetal genes were most important for birth length and head circumference.