Objective: Intrauterine nutrition approximated by birth weight has been shown to be inversely associated with risk of coronary heart disease (CHD). By investigating the association within twin pairs discordant for disease, the influence of genetic and early environmental factors is substantially reduced.
Methods: We have investigated the association between birth weight and angina pectoris in same-sexed twins with known zygosity included in the population-based Swedish Twin Registry. Self-reports of birth weight and angina pectoris were collected in a telephone interview between 1998 and 2000. The cohort analyses were based on 4594 same-sexed twins, and the within-pair analyses included 55 dizygotic and 37 monozygotic twin pairs discordant for angina pectoris. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by logistic regression.
Results: Compared with birth weight between 2.0 and 2.9 kg, low birth weight (<2.0 kg) was associated with increased risk of angina pectoris in the twin cohort, (OR: 1.46; 95% CI: 1.14-1.87), but after adjustment for potential confounders the risk decreased, and did not reach significance. Within twin pairs discordant for angina pectoris, low birth weight was significantly associated with increased risk of angina pectoris within dizygotic twins (adjusted OR: 5.73; 95% CI: 1.59-20.67), but not within monozygotic twins (adjusted OR: 1.20; 95% CI: 0.40-3.58).
Conclusions: The results suggest that genetic differences associated with foetal growth and adult risk of CHD may have affected previously reported associations between birth weight and CHD.