Posttest risk calculation following positive noninvasive prenatal screening using cell-free DNA in maternal plasma

American Journal of Obstetrics and Gynecology
Peter Benn

Abstract

Noninvasive prenatal screening (NIPS) for fetal chromosome defects has high sensitivity and specificity but is not fully diagnostic. In response to a desire to provide more information to individual women with positive NIPS results, 2 online calculators have been developed to calculate posttest risk (PTR). Use of these calculators is critically reviewed. There is a mathematically dictated requirement for a precise estimate for the specificity to provide an accurate PTR. This is illustrated by showing that a 0.1% decrease in the value for specificities for trisomies 21, 18, and 13 can reduce the PTR from 79-64% for trisomy 21, 39-27% for trisomy 18, and 21-13% for trisomy 13, respectively. Use of the calculators assumes that sensitivity and specificity are constant for all women receiving the test but there is evidence that discordancy between screening results and true fetal karyotype is more common for older women. Use of an appropriate value for the prior risk is also important and for rare disorders there is considerable uncertainty regarding prevalence. For example, commonly used rates for trisomy 13, monosomy-X, triploidy, and 22q11.2 deletion syndrome can vary by >4-fold and this can translate into large differences in PT...Continue Reading

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Citations

Dec 6, 2016·Scientific Reports·Birgit Sikkema-RaddatzGerard J Te Meerman
Jun 19, 2018·Expert Review of Molecular Diagnostics·Elisa BevilacquaJacques C Jani
Nov 18, 2016·F1000Research·Ignatia B Van den Veyver

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22q11 Deletion Syndrome

22q11.2 deletion syndrome, also known as DiGeorge syndrome, is a congenital disorder caused by a partial deletion of chromosome 22. Symptoms include heart defects, poor immune system function, a cleft palate, complications related to low levels of calcium in the blood, and delayed development. Discover the latest research on this disease here.