Genetic influence on birthweight and gestational length determined by studies in offspring of twins

TLDR

Genetic influences on birthweight and gestational length may be partly mediated by maternal anthropometry, lifestyle, and pregnancy complications, though the study does not separate fetal from maternal genetic effects. The study aims to quantify the relative importance of genetic effects on birthweight, gestational length, and small‑for‑gestational‑age status. A cohort of 868 monozygotic and 1,141 dizygotic female twin pairs born before 1959 was analyzed using quantitative genetic methods on linked Swedish Twin and Birth Registers to estimate twin similarities in birthweight, gestational length, and small‑for‑gestational‑age outcomes via concordance rates and intra‑class correlations. Monozygotic twins showed consistently higher concordance rates and intra‑class correlations for birthweight, gestational length, and small‑for‑gestational‑age, yielding heritability estimates of 25–40 % and indicating genetic effects on birthweight, fetal growth, and gestational length.

Abstract

Objective To determine the relative importance of genetic effects on birthweight, gestational length and small for gestational age. Design A cohort study, using individual record linkage between the population‐based Swedish Twin and Birth Registers to estimate twin similarities in twins with known zygosity. Population Included were 868 monozygotic and 1141 dizygotic female twin pairs, born in Sweden before 1959, who both delivered single births from 1973–1993. Methods Quantitative genetic methods, offspring birthweight, gestational length and small for gestational age birth in twin sisters. Main outcome measures Twin similarities measured as probandwise concordance rates and intra‐class correlations for birthweight, gestational length and small for gestational age births. Results Concordance rates and intra‐class correlations for birthweight, gestational length and small for gestational age were consistently higher in monozygotic compared with dizygotic twins. Model fitting suggested heritability estimates in the range from 25% to 40%. Conclusions This study suggests genetic effects not only for birthweight and fetal growth, but also for gestational length. The mediation of these genetic effects may partly be due to similarities in maternal antropometric measures, lifestyle and medical complications during pregnancy. The study does not distinguish between fetal and maternal genetic effects.