How reliable is Non-Invasive Prenatal Testing compared to conventional screening

[Anonymous]

How reliable is Non-Invasive Prenatal Testing compared to conventional screening methods?

[Sana Fathima K S]

For trisomy 21, Non-Invasive Prenatal Testing achieves substantially higher sensitivity and a lower false-positive rate than conventional first-trimester combined screening, which is based on maternal age, nuchal translucency measurement, and biochemical markers. Sensitivity for trisomy 21, trisomy 18, and sex chromosome aneuploidies generally exceeds 97 to 100 percent, with specificity above 99 percent, in large validation cohorts. However, the positive predictive value varies significantly by condition: it is highest for trisomy 21 (commonly cited around 80 to 85 percent in tested populations), progressively lower for trisomy 18 and trisomy 13, and lowest for rare autosomal aneuploidies and copy number variants (often in the single digits to low double digits). This distinction is clinically important, a high-probability result on a genome-wide panel for a rare autosomal aneuploidy carries a much greater chance of being a false positive than the same result for trisomy 21. No screening test offers 100 percent accuracy, and a no-call or inconclusive result can occur due to insufficient fetal fraction. Every high-probability result should be routed through genetic counseling and confirmed with a diagnostic test before any decision regarding the pregnancy is made.

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