• Evaluation of Fetal Nuchal Translucency Threshold Alternatives for Down Syndrome Diagnosis
  • Nasrollah Saleh-Gohari,1 Seyedeh Sepideh Aghamirli,2 Marzieh Khalouei,3,*
    1. Department of Medical Genetics, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran.
    2. Department of Medical Genetics, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran.
    3. Department of Medical Genetics, Faculty of Medicine, Kerman University of Medical Sciences, Kerman, Iran.


  • Introduction: One of the most common and well-known chromosomal disorders is Down syndrome (DS). DS is the most frequent genetic explanation of mild mental retardation. DS prenatal screening has been incorporated into Iran's prenatal care and consideration programs. The objective of the present study was to investigate the relationship between prenatal screening results (Trisomy 21 risk and nuchal translucency) and amniocentesis karyotype results to report the new nuchal translucency (NT) cut-point as a first trimester triage marker for pregnant women.
  • Methods: In this present prospective study, a total of 363 pregnant women were evaluated from March 2020 to March 2022 in Kerman, Iran. According to their prenatal screening test by determining the risk of trisomy 21 (combination of maternal serum levels of Alpha-fetoprotein, unconjugated estriol, and human chorionic gonadotropin multiples of the normal median (MoM) results with maternal age) and NT, the amniocentesis test had been done for each pregnant woman. Amniotic fluid cell culturing and karyotype analysis had been done. Moreover, the data were analyzed using descriptive and inferential statistical methods (SPSS Statistics software version 26).
  • Results: Positive combined prenatal screening for DS is when NT thickness overextended 4.0 mm. As pregnant women age, their gestational age changes this upper NT threshold value. In other words, the NT clinical test has a significant relationship with DS developing in fetuses (P-Value < 0.001). The best cut-point for NT clinical test was number 2.2050 and the sensitivity and specificity of this test were equal to 0.647 and 0.852, respectively. The laboratory test of DS had a significant correlation with Down syndrome risk (P-Value < 0.001). The best cut-point value for DS laboratory test (Trisomy 21 risk test) was 0.032 level, and the sensitivity and specificity of this test are 0.786 and 0.843, respectively. Also, one unit increase in Trisomy 21 (T21) Risk increased the possibility of developing DS by 18.11 times (P-Value = 0.013). The chance of developing DS in male fetuses was equal to in female fetuses (P-Value = 0.067).
  • Conclusion: The current study determined the association between prenatal screening results (risk of T21 and NT) and amniocentesis karyotype results and indicated possible alternatives for cut-points to DS and NT risks. Also, the two sexes were affected approximately equally. The present research provides insight into the most appropriate indications for NT value to apply in Iran's laboratories.
  • Keywords: Down Syndrome, Screening test, Nuchal translucency, Amniocentesis, Diagnosis.