What Are the Threats to Accuracy in Non-Invasive Prenatal Testing?

Threats to accuracy in non-invasive prenatal testing (NIPT) include a sample that’s too small, too old, or doesn’t contain enough fetal DNA and the mother’s weight. Patricia Geraghty, NP, explains all the threats to accuracy in NIPT in this video.

Transcript

00:00

Well, I think the general population feels that noninvasive prenatal testing is essentially perfect.

00:06

And the health care professionals maybe think it's not at all perfect. And probably, the answer is somewhere in between.

00:13

But some of the things that can make the answer that you receive from noninvasive prenatal testing incorrect

00:21

would be the sample itself. Say the sample's too old when it gets to the lab or there isn't enough sample drawn.

00:28

It can be what's in the sample. If there isn't enough fetal DNA present, then they either can't run it-- we expect about 10% to 15%

00:39

of the blood to show fetal DNA. And if it's less than 4%, they either can't do the test at all.

00:45

Or if they do it, it has the possibility of actually missing a problem. Some of the things that might decrease

00:52

the amount of fetal DNA present is if the test is being done too early. It's done between 10 weeks of gestation,

00:58

10 weeks of pregnancy, and 33 weeks of pregnancy. But if perhaps, you're a little earlier than that maybe they won't be in a fetal DNA.

01:06

Another thing is mom can change it. Women who are overweight have a lower fraction of fetal DNA.

01:14

Why? Because in addition to mom's blood cells and giving her own DNA into her blood,

01:22

there's also fat cells that are breaking down. And so the fat cells are adding an extra component of maternal DNA.

01:29

And that reduces the amount of fetal DNA we have to look at. And then, finally, the fetus can make a difference too.

01:35

It's some genetic problem changes, some genetic changes. For example, trisomy 21 or three 21st chromosomes,

01:44

we have a higher percentage of fetal DNA. But in trisomy 18, or three 18 chromosomes,

01:50

the percentage of fetal DNA is down. And that's what can allow us to mistakenly miss a trisomy 18 sometimes.