ABSTRACTObjectiveThis study aims to evaluate the prevalence of congenital heart disease (CHD) in monochorionic (MC) twin pregnancies with and without twin‐to‐twin transfusion syndrome (TTTS) in an unselected cohort, which underwent prenatal and postnatal echocardiography.MethodThis was a retrospective cohort study including 451 MC twin pregnancies between 2002 and 2012. Complete outcome data were available for 381 pregnancies. All patients had prenatal echocardiography, and postnatal echocardiography was performed in all newborns with symptoms or to follow‐up on prenatal findings. Data from prenatal and postnatal echocardiography and autopsy were analyzed. The classification of Houyel et al. was used for structural CHD.ResultsStructural CHD was diagnosed in 5.5% of all MC twins (42/762). Twins with TTTS showed a significant higher rate of CHD than unaffected twins (9.3% vs 4.7%; p = 0.03). Prenatal detection rate of CHD was 48%. Most common abnormalities were ventricular septal defects (VSD) (2.1%) followed by anomalies of the ventricular outflow tracts (1.3%) in the overall population and VSD (2.9%) and anomalies of the great arteries (2.9%) in the group with TTTS.ConclusionMC twin pregnancies show a high prevalence of structural CHD (5.5%), especially those affected by TTTS. A detailed prenatal and postnatal echocardiography could be considered in these pregnancies. © 2014 John Wiley & Sons, Ltd.