Targeted ultrasonographic screening for nuchal fluid accumulation during the first trimester (9-13 weeks) seems to be a recommendable method for the detection of Down's syndrome and other chromosomal anomalies in pregnant women. It compares favorably with current methods of maternal serum screening performed during the second trimester. Using a 4-mm cut-off value, the detection rate of aneuploidy among our population was found to be 57.1%, with a false-positive rate of 0.7% and a positive predictive value of 72.7%. Chromosomal analysis should be considered for fetuses with nuchal translucency equal to or greater than 4 mm in the first trimester.