Objective: To determine the utility of the first-trimester fetal nuchal translucency (NT) thickness in the prediction of fetal cardiac malformations. Design: Retrospective study. Setting: Department of Obstetrics and Gynecology and Medical Genetics, University of Szeged. Methods: The pre-and postnatal course and outcome, and the relationship between the first-trimester fetal NT thickness and fetal congenital heart defects (CHDs) in 4309 pregnancies ended up with birth or therapeutic abortion between January 1998 and June 2000 were registered. Prenatal care included first-and second-trimester fetal sonography at weeks 10-13 and 18-20, respectively. Results: 4251 births and 58 first-and second-trimester therapeutic abortions due to lethal congenital malformations or chromosomal abnormalities were recorded. Altogether 209 (4.9%) congenital malformations were detected, 39 (18.7%) of which were heart defects with normal karyotype. At birth, 151 congenital malformations were diagnosed, 34 of them were known prenatally. The prevalence of CHDs was 9 per 1000 pregnancies. The measurement of fetal NT thickness was available in 35 of the 39 fetuses with heart defects: it was !3 mm in 18 (51.4%) and <3 mm in 17 (48.6%). A sensitivity of 51.4% was found at a cutoff of 3 mm. Conclusions: An increased NT thickness in chromosomally normal fetuses was found to be highly associated with CHDs and identified in more than half of the affected cases. Furthermore, an increased NT of !3 mm can be regarded a selection criterion for early second-trimester targeted fetal echocardiography and for increased fetal and neonatal surveillance. #