Sensitivity and specificity of a prenatal screening method using the combination of maternal age and fetal nuchal translucency thickness for fetal aneuploidy: a clinical study in eastern India

Background: Down’s syndrome (DS), one of the commonest fetal aneuploidy, is associated with mental retardation and physical disabilities in the affected individual. The aim of this study is to determine the sensitivity and specificity of a screening method using the combination of maternal age and fetal nuchal translucency thickness for all fetal aneuploidy including DS in our population.Methods: All 412 mothers, in this retrospective study, had an ultrasound scan between 11 weeks and 13 weeks 6 days of gestation when nuchal translucency thickness of the fetus was measured. The individual risk of each mother was calculated using a software that takes maternal age, nuchal translucency thickness and crown-rump length into consideration. Using a cut-off risk estimate of 1 in 300, the women were grouped into screen positive and screen negative. The chromosomal status of all the fetuses were checked either by amniocentesis and chromosomal study or by birth of a phenotypically normal child. Sensitivity and Specificity of the screening method were calculated from the available data.Results: Sensitivity of the screening test for fetal trisomy 21 was 75% and for all fetal aneuploidy was 80 %. Specificity of the screening test for all fetal aneuploidy was 91.4% and False Positive Rate was 8.6 %. Our results are consistent with the results obtained in other large international studies.Conclusions: Combination of maternal age and fetal nuchal translucency thickness is an effective prenatal screening method for fetal aneuploidy