Objective: Increased nuchal translucency (NT) at the 11 -14 week scan has been shown to be associated with chromosomal anomalies and congenital heart disease. The rate of association has varied between 17 and 56% in different publications and suggested there is no link between increased NT and specifi c types of congenital heart disease (CHD). Our aim was to explore these aspects in more detail. Methods: All fetuses with CHD, seen during a 9-year period between 1998 and 2006, were identifi ed

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... trospectively from King's College (KCH) and Evelina Children's Hospital (ECH) databases. Data collected included the type of CHD, the NT measurement and the karyotype at each centre. Results: There were 1626 fetuses with CHD where the NT measurement was known. The karyotype was known in 1102 of these. Of 536 fetuses with known normal chromosomes the NT was increased in 43%. Of 566 fetuses with known chromosomal abnormalities, NT was increased in 73%. The incidence of increased NT was higher in the KCH group than in the ECH group, this was related to the higher incidence of karyotype anomalies in the former group. Because of this, only cases with a known normal karyotype were included in the analysis. Five categories of CHD were chosen for more detailed study, coarctation of the aorta, hypoplastic left heart syndrome, transposition of the great arteries, atrioventricular septal defect and tetralogy of Fallot. Of 119 cases with coarctation, 52 had an increased NT (44%). Of 60 cases of the hypoplastic left heart syndrome, 24 had an increased NT (40%). Of 92 cases of transposition, 29 had an increased NT (31%). Of 59 cases of atrioventricular septal defect, 32 had an increased NT (54%). Of 104 cases of tetralogy of Fallot, 40 cases had an increased NT (40%). Conclusion: Major CHD is associated with increased NT in 30 -54% of cases. The rate of association varies with the type of CHD present. Studies which examine this connection must exclude fetuses with chromosomal anomalies as these fetuses will skew the results, and must have suffi ciently large groups of different types of CHD to make meaningful observations. O1-2 Preventive effect of periconceptional folic acid supplementation on the risk of congenital heart defects: A registry based case-control study in