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.