Relationship between nuchal translucency thickness and prevalence of major cardiac defects in fetuses with normal karyotype.

OBJECTIVE To define the prevalence of major cardiac defects according to nuchal translucency (NT) thickness at the 11 to 13 + 6-week scan in fetuses with normal karyotype. METHODS Specialist fetal echocardiography was carried in 6921 fetuses with normal or presumed normal karyotype at a median gestation of 20 (range 12-35) weeks. The indications for fetal echocardiography were increased NT thickness (n = 3444), detailed second-trimester scan either for assessment of risk of chromosomal abnormalities (n = 2980) or previous or family history of fetal defects (n = 497). The cardiac defects were grouped into six functional categories: septal defect, left inflow obstruction, right inflow obstruction, left outflow obstruction, right outflow obstruction and other. RESULTS Major cardiac defects were identified in 132 (19.1 per 1000) fetuses and the prevalence increased with fetal NT thickness from 4.9 per 1000 in those with NT below the median, to 8.7 for NT between the median and less than the 95th centile, 18.2 for NT between the 95th and 99th centiles, and exponentially thereafter to 35.2, 64.4 and 126.7 for respective NTs of 3.5-4.4 mm, 4.5-5.4 mm and > or = 5.5 mm. There was no obvious difference in the distribution of NT in the different types of cardiac defects. CONCLUSIONS The prevalence of major cardiac defects increases exponentially with fetal NT thickness and in fetuses with NT of 3.5 mm or more it is higher than in pregnancies with a family history of cardiac defects.