Value of Nuchal Translucency in Detection of Chromosomal Aberrationin Vietnam Population

Abstract

Objective: To examine the sensitivity and specificity of different thresholds of nuchal translucency in diagnosis of chromosomal defects.
Study Design: This is a longitudinal study of pregnant women have first trimester screening and ultrasound in center of diagnostic antenatal of national hospital of obstetrics and gynecology. A follow-up was made to identify, in all singleton pregnancies in both group of which fetal karyotyping was made and group of normal fetuses. The threshold for nuchal translucency was divided in to above the 95th percentile, the 99th percentile, the 3.0mm and 2.5 MoM
of nuchal translucency. The sensitivity and specificity ware calculated in order to diagnosis the chromosomal abbreviation.
Results: The research identified 2645 fetuses, 743 amniocentesis (28%). There is 32.4% fetus has NT ≥ the 95th percentile, 28.6% ≥ 2.5mm percentile, 22.3% ≥ 3.0mm, 16.6% above 2.5 MoM. The fetal karyotype was abnormal in 157 (5.8%) pregnancies. The popular conditions were found including trisomy 21(52.2%). Then structural rearrangements occupied 31.2%. Other chromosomes like 13,18,21 occupied 12.7%. The abnormal of sex chromosome was smallest proportion with only 3.8%. At the 95th percentile of nuchal translucency has the highest sensitivity in detection of chromosomal defects (99.4%) but the threshold 2.5mm has a better detection rate (20.4%). The cut off 3.0mm has a better positive prediction rate (22.3%) but could detect less defects (only 132/157 abbreviation). The threshold 2.5xMoM had the highest specificity (86.4%) but lowest sensitivity (only 65%).
Conclusion: In fetuses with increased nuchal translucency, more than a half of the chromosomally abnormal group is affected by defects other than trisomy 21 (52.2%). Using threshold 2.5mm helps detect more 23 chromosomal defects in comparison with the threshold 3.0mm and it had the highest average of sensitivity and specificity (87.25%).