Ultrasound Obstet Gynecol 2011; 38: 320–324 Published online 7 July 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.8977 Prenatally detectable congenital heart defects in fetuses with Down syndrome R. MOGRA, V. ZIDERE and L. D. ALLAN Harris Birthright Research Centre for Fetal Medicine, King’s College Hospital, London, UK KEYWORDS: congenital heart defect; Down syndrome; prenatal diagnosis; ultrasound ABSTRACT Objective To document the incidence of congenital heart defects (CHD) that are detectable echocardiographically in the fetus with trisomy 21 and the relationship with nuchal translucency, fetal sex and ethnicity. Methods Data on fetuses with a karyotypic diagnosis of trisomy 21 were collected between January 2002 and March 2010. The data were analyzed for the gestational age at examination, maternal age, reason for referral for fetal echocardiography, cardiac diagnosis, fetal sex, ethnicity and outcome. Results Of 917 fetuses with trisomy 21, 487 had a diagnostic echocardiogram. Cardiac examination was performed before 14 weeks’ gestation in 75% of cases. The main reasons for referral were increased nuchal translucency (NT) in 76% of cases, suspected cardiac abnormality in 15% and an extracardiac anomaly in 6%. Structural CHD was found in 164/487 (34%), or 98/412 (24%) if those referred for suspected CHD are removed from the analysis. The most common diagnosis was atrioventricular septal defect (AVSD) (115/487, 24%). The ratio of female to male fetuses with AVSD was 29% : 18% (P = 0.003). There was no difference in the incidence of AVSD with ethnicity. The pregnancy continued in 36 cases, but three were lost to follow-up; of the known outcomes there were 10 intrauterine deaths, six of which had structural heart disease, and 23 live births, 15 of which had CHD. Conclusion Most fetuses (66–76%) with trisomy 21 have a structurally normal heart on echocardiography. The presence of structural CHD was not associated with increased NT. The increased incidence of AVSD in females was confirmed in our study, although an ethnic difference could not be confirmed. CHD does not appear to increase the chance of spontaneous intrauterine loss in ongoing pregnancies. Copyright  2011 ISUOG. Published by John Wiley & Sons, Ltd. INTRODUCTION It is commonly suggested in the literature that most children or fetuses with Down syndrome have congenital heart disease (CHD). Data from detailed examinations of affected children contradict that, however, with CHD found in only about 40% of cases 1–6 . An atrioventricular septal defect (AVSD) is well recognized as the most common form of CHD, occurring in about 20% of the total Down group or half the group with CHD. Ventricular septal defects (VSD), secundum atrial septal defects (ASD) and persistent arterial duct (PDA) make up the majority of the rest of the cases of CHD in children 7–9 . Some VSDs are large and therefore might be detectable prenatally but ASDs and PDAs, of course, are not detectable in the fetus. Tetralogy of Fallot and coarctation occur in small numbers in postnatal series and one would expect these to be detectable in the fetus. Confounding the data concerning the incidence of CHD postnatally is that an aberrant right subclavian artery (ARSA) is much easier to detect (if looked for) in the fetal than in the postnatal echocardiogram 10–12 . This abnormality therefore is likely to be under-reported in postnatal echocardiography series, although it has been reported in earlier catheter and postmortem series in Down syndrome 1,13–16 . Our aim was to document the incidence of structural CHD detectable in Down syndrome fetuses using recent knowledge and equipment, and to explore the relationship of CHD in trisomy 21 with nuchal translucency (NT), fetal sex and ethnicity. Correspondence to: Prof. L. D. Allan, Harris Birthright Unit, 3rd Floor Golden Jubilee Wing, King’s College Hospital, London SE5 9RS, UK (e-mail: lindsey.allan2@btinternet.com) Accepted: 15 February 2011 Copyright  2011 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER