Twinship influence on morbidity and mortality across the lifespan.

BACKGROUND Studies in twins may be questioned with respect to their representativeness of the general population, not least considering the potential importance of the fetal environment for future health and disease. To better understand the influence twinning may have on health, we investigated long-term health outcomes of twins, their singleton siblings and singletons from the population. METHODS Morbidity and mortality in twins was contrasted to that of their singleton siblings. These singletons from families with twins were then compared with singletons of the population to further reveal potential twin family influences on health. Familial relations were identified through the Swedish Multi-Generation Register. Among individuals born between 1932 and 1958, the number of twins and their singleton siblings identified were 49,156 and 35,277, respectively. Outcomes were incident overall cancer, cardiovascular disease (CVD) and death, identified in national registers. Standardized survival functions were estimated using Cox proportional hazards regression and the corresponding cumulative risks plotted against age. RESULTS Cumulative risks of cancer, CVD and death in twins did not differ from singletons of families with twins, who in turn were found to be similar to singletons of families without twins. As could be expected from these findings, no differences in risks were found when twins were compared with singletons of the population. CONCLUSIONS Despite their adverse intrauterine experience, twins do not seem to fare worse than singletons with respect to adult morbidity and mortality. The findings indicate that the unique experience of twinning does not lead to adverse long-term health outcomes.