Prenatal diagnosis of fetal aneuploidy is a continuously and rapidly evolving area of research. Currently in the United States, the standard of care for screening pregnancies for aneuploidy involves assessment of maternal age together with the use of multiple second trimester maternal serum markers. This screening approach identifies approximately 60% of pregnancies with fetuses affected with Down syndrome and provides results in the second trimester of pregnancy. First trimester screening for aneuploidy by using nuchal translucency sonography is one of the most promising areas of research in the detection of Down syndrome. This screening method involves measuring the normal space located between the cervical spine and overlying fetal skin at 10 to 14 weeks' gestation. Studies from both high risk and unselected patient populations suggest significant advantages to this approach for Down syndrome detection compared with currently available second trimester screening methods. The combination of first trimester biochemical screening and nuchal translucency measurements may further improve the efficacy of prenatal screening for aneuploidy. The article reviews studies suggesting a role for nuchal-translucency-based aneuploidy screening and describes areas of ongoing research in this field.