Genetic and maternal environmental contributions to estimated fetal weight at 20 weeks gestation compared with birthweight

The study examined 3110 mother-child pairs from three population cohorts in the United Kingdom and China to understand how genetic and environmental factors influence fetal growth. Researchers measured estimated fetal weight at 20 weeks gestation and birthweight, analyzing the impact of fetal sex, genetic birthweight scores, maternal BMI, glucose levels, smoking, maternal age, and parity. All examined factors were associated with fetal weight in both periods, except maternal glucose levels and smoking, which affected only birthweight. Male fetal sex and higher maternal genetic score were consistently associated with higher weight in both periods. Fetal genetic factors and some maternal factors showed more pronounced effects later in pregnancy. The findings suggest that the timing of clinical monitoring of fetal growth should account for the varying influences of these factors at different stages of pregnancy.