Fetal nuchal translucency: ultrasound screening for chromosomal defects in first trimester of pregnancy.

OBJECTIVE To examine the significance of fetal nuchal translucency at 10-14 weeks' gestation in the prediction of abnormal fetal karyotype. DESIGN Prospective screening study. SETTING The Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London. SUBJECTS 827 fetuses undergoing first trimester karyotyping by amniocentesis or chorionic villus sampling. MAIN OUTCOME MEASURE Incidence of chromosomal defects. RESULTS The incidence of chromosomal defects was 3% (28 of 827 cases). In the 51 (6%) fetuses with nuchal translucency 3-8 mm thick the incidence of chromosomal defects was 35% (18 cases). In contrast, only 10 of the remaining 776 (1%) fetuses were chromosomally abnormal. CONCLUSION Fetal nuchal translucency > or = 3 mm is a useful first trimester marker for fetal chromosomal abnormalities.