Accuracy of the Combined FirstTrimester Down Syndrome Screening Test and the Optimum Range of the Cut-off Point for Intermediate-risk Identification: Twelve years’ experience

Abstract

Objectives: This study aimed to determine the performance of the combined first trimester Down syndrome screening test and the appropriate cut-off points for intermediate-risk identification. Materials and Methods: This was a retrospective study conducted from May 2019 to May 2021. All the medical charts of women with singleton pregnancy who had a first-trimester combined screening test performed between 2007 - 2018 were reviewed. A total of 3,928 women with singleton pregnancy were included in the final analysis. Data regarding neonatal outcomes were recorded, and a telephone follow-up was performed with the women who had given birth elsewhere. Statistical analysis was performed using SPSS version 18.0 software. Results: With a high-risk cut-off point of 1:250, the test had a sensitivity of 75%, and a specificity and accuracy of 94%. When an intermediate-risk cut-off point between 1:500 and 1:1,000 was applied, the specificity and accuracy increased to 83% - 90%. When using a cut-off point between 1:251 and 1:1,000, the specificity and accuracy was 83%, while the rate of intermediate risk was 11.6%. Conclusion: Our combined first-trimester screening test had a detection rate of 75%, and a high specificity and accuracy of 94%. The recommended cut-off point for intermediate risk was between 1:251 and 1:1,000, since this offered good specificity and accuracy with an acceptable rate of intermediate risk.