A prospective study was conducted to determine the cut-off values of nuchal skin-fold thickness (NFT) with false-positive rates for each gestational week (GW) for chromosomal abnormalities during the 2nd trimester of pregnancy. A total of 2,313 women with normal singleton pregnancies were included in the study. Cases of multiple gestations, aneuploidy and major congenital malformations were excluded. The distribution of NFT between the 15th and 24th GW and the cut-off values of NFT with false-positive rates for chromosomal abnormalities were determined. A significant positive correlation was noted between NFT and GW. Statistically significant differences were observed in NFT for the each GW. The 95th percentile values of NFT between 15 and 24 weeks' gestation were 4.7, 4.77, 5.0, 5.5, 5.76, 5.9, 6.0, 6.1, 6.5 and 6.8 mm, respectively. In all fetuses, if the cut-off value of NFT was considered as 6 mm, the false-positive rate ranged from 1.8% to 37% in 15-24 weeks' gestation. Evaluation of NFT according to cut-off values determined by population-based percentiles for each GW might be a more appropriate screening method for chromosomal abnormalities than accepting NFT >= 6 mm for all fetuses as abnormal, regardless of gestational age.