Why there are False Positives with
Non Invasive Prenatal Testing (NIPT)
2 Cells multiply
1 Fertilisation occurs
HOWEVER,
3 Embryo develops
!
BUT UP TO 1% OF THE TIME . . .
when the cells multiply, a trisomy event occurs
but only in the outer layer of the placenta
(trophoblast), whereas the fetus remains normal.
in a study on 11,105 pregnant women,
99.96% OF THE TIME . . .
This is due to a self correcting mechanism
(trisomic rescue) in which the fetus “expels”
the cell(s) with the extra chromosome,
thereby developing normally.
accurately detected
· Down Syndrome (T21)1
· Edwards Syndrome (T18)1
· Patau Syndrome (T13)
with the lowest false positive rate of 0.04%.
1
Shan Dan et al. Prenatal Diagnosis 2012, 32, 1-8
4 Trisomic DNA appears in
mother’s blood
Trisomic trophoblast
(placental) DNA
Mother’s
cell
5 Non Invasive prenatal testing
The cell-free fetal DNA (cffDNA) collected from the
mother’s blood picks up this Trisomic DNA, thereby
showing a false positive result for abnormality (e.g.
Down Syndrome) when the fetus is actually normal.
Healthy
fetus DNA
Amniocentesis
In the case of Confined Placental Mosaicism,
only amniocentesis testing will return the actual
result that the fetus is normal.
This information is meant to highlight why false positives occur in NIPTs in general.
A false positive means that a baby who is thought to have a genetic disorder by NIPT is then
born normal (without the disorder). iGeneTM has the lowest false positive rate of 0.04%.
For more information, please visit www.igeneprenatal.com.
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