Screening for fetal cardiac defects is traditionally based on the ultrasonographic examination of the four-chamber view of the fetal heart at mid-gestation, which has been shown to identify 26% of major cardiac defects. Pathological studies in fetuses with increased nuchal translucency at 10-14 weeks of gestation, a sonographic marker for chromosomal abnormalities, have shown an association between increased nuchal translucency and congenital abnormalities of the heart. This study reports the prevalence of cardiac defects in 1427 chromosomally normal fetuses with increased nuchal translucency thickness, and examines the potential value of this sonographic marker in screening for major cardiac defects. The diagnosis of cardiac defects was made either by postmortem examination in terminations of pregnancy and intrauterine or neonatal deaths or by clinical examination and appropriate investigations in live births. The prevalence of major cardiac defects was 17 per 1000 (24 of 1427 fetuses) and increased with translucency thickness from 5.4 per 1000 for translucency of 2.5-3.4 mm to 233 per 1000 for translucency of > or = 5.5 mm. These findings suggest that measurement of nuchal translucency thickness at 10-14 weeks may prove to be a useful method of screening for abnormalities of the heart and great arteries in addition to its role in screening for chromosomal defects.