Increased Prevalence of Congenital Heart Defects in Monozygotic and Dizygotic Twins

Study Questions:

What is the occurrence of congenital heart disease (CHD) in monochorionic and dichorionic twins as compared with singletons?


A registry-based study was used, linking the Danish Twin Registry, National Birth Register, and the Danish National Patient Register. Sensitivity analyses were performed to mitigate the impact of prematurity and subsequent increased risk of patent ductus arteriosus.


Among 41,525 twin individuals, a total of 584 twins (1.4%) had a congenital heart defect diagnosis in the National Patient Register, as compared with 648 out of 74,473 (0.87%) singletons (p < 0.001). Patent ductus arteriosus and coarctation of the aorta were particularly common, occurring more than three times as often in twins as in singletons: 3.9 (95% confidence interval [CI], 2.6-5.8) and 3.1 (95% CI, 1.5-6.4), respectively. There was not a higher risk for CHD among monozygotic twins compared to dizygotic twins, and the CHD was also increased in dizygotic twins. When all preterm twins were excluded, the risk for CHD remained increased at 21% (95% CI, 3-42%) as compared with a 63% increase seen in the initial analysis (95% CI, 45-82%).


The authors concluded that CHD is more common in both monochorionic and dichorionic twins as compared with singletons.


This study demonstrated increased risk of CHD in twins, which interestingly, was not restricted to monochorionic twins. Previous studies have suggested monochorionicity as the central mechanism for the increased risk of CHD, particularly in twins impacted by twin-to-twin transfusion syndrome. When premature infants were removed from analysis, the risk of CHD remained, but appeared to be lower. The primary unresolved issue which emerges from this study would be the mechanism of increased risk for CHD in twins if it is not monochorionicity.

Clinical Topics: Congenital Heart Disease and Pediatric Cardiology, Congenital Heart Disease

Keywords: Heart Diseases, Prevalence, Heart Defects, Congenital

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