Comparison of Late Mortality Among Twins Versus Singletons With Congenital Heart Defects

In 2014, in the United States, nearly 7% of newborns were twins. Congenital heart defects (CHDs) are more frequent in both monozygotic and dizygotic twins than in singletons. Still, the longer-term prognosis for CHD twins is unknown. Here we assess the mortality pattern for CHD twins up to age 36 years and compare it with that for non-CHD twins, non-CHD co-twins, and CHD singletons. We identified all twins and a 5% random sample of all singletons born in Denmark from 1977 to 2009 by linking Danish national population and health registers. CHD cases were defined as subjects having a primary inpatient diagnosis of CHD (excluding preterm ductus) within the first year of life, and mortality was assessed through 2013. Among 63,362 live-born twin individuals, a total of 373 twins (0.59%) had a CHD diagnosis, whereas the corresponding numbers for singletons were 383 of 98,647 (0.39%). During the follow-up, 82 (22.0%) CHD twins died compared with 91 (23.8%) CHD singletons (p = 0.56). Despite a 5 times higher proportion of prematurity, CHD twins had a tendency toward only a moderately increased neonatal mortality compared with CHD singletons (hazard ratio 1.5, 95% confidence interval 0.94 to 2.5), and after the neonatal period up to age 36 the tendency was reversed (hazard ratio 0.8, 95% confidence interval 0.5 to 1.2). A potential underlying mechanism for this mortality pattern is selective intrauterine and neonatal mortality of twins with the most severe CHD. In conclusion, the study indicates that the overall survival prognosis for CHD twins is similar to that of CHD singletons.