Reference values of nuchal fold thickness in an Iranian population sample.

BACKGROUND: Considering that ethnicity and gestational age (GA) could affect the value of nuchal fold thickness (NFT) in mid-trimester, we aimed to determine the reference intervals of NFT values for each gestational week from 16 to 24 weeks of pregnancy among a group of Iranian pregnant women.

MATERIALS AND METHODS: In this cross-sectional study, medical files of pregnant women who underwent fetal anomaly scanning at 16-24 weeks of gestation were reviewed and the following data were extracted: GA, value of NFT, value of nuchal translucency (NT) in their previous ultrasound study, if available, and head circumference (HC). The 5th , 25th , 50th , 75th , and 95th percentiles of NFT for each gestational week were determined. The association between NFT and HC, GA, and NT were also determined.

RESULTS: Medical files of 882 pregnant women were studied. The expected 95th percentile value of NFT between 16th and 24th weeks of gestation ranged from 4 mm to 5.9 mm. The mean (standard deviation) of NFT increased with GA from 2.67 (0.90) mm at 16th weeks to 4.69 (0.71) mm at 24th weeks. There was a significant positive association between NFT and GA (β = 1.11, p < 0.001), HC (β = 0.21, p < 0.001), and NT (β = 0.351, p < 0.001).

CONCLUSION: The findings of this study revealed that before the 20th week of gestation, the appropriate cutoff value of NFT is 5 mm, and for 21st to 24th weeks, the proper cutoff is 6 mm. However, for providing more conclusive results, further studies with larger sample size and considering the impact of other influencing variables are recommended.