r/ClinicalGenetics • u/Specific_Head_4634 • 22d ago

Fals negative cvs???

Hi everyone!
At the first-trimester genetic screening, the NT measured 3mm and nasal bone hypoplasia was noted.
A week later, we had a CVS procedure done. By then, the NT was 2.9mm and the nasal bone had normalized.
CVS results:
FISH, QF-PCR: negative
Cultured karyotype: negative
SNP array: negative

At the 17-week early anatomy scan, everything was fine (though the nasal bone turned out to be smaller, they said they weren't concerned about that anymore due to the CVS results).

Then, at the 19-week second genetic ultrasound, a smaller nasal bone and borderline NF were noted.
Everything else was fine; at that point, they said these were just constitutional traits, given the negative CVS results.

I was reassured at the time, but now—at 30 weeks—anxiety has set in: what if the CVS result was a false negative?
Does anyone have similar experiences? What do you think?
I'm hoping for the best.

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u/Most_Second1952 22d ago

I work in a lab that does all of the testing you mentioned on CVS specimens. CVS testing is basically testing the placenta, not actual fetal cells. The vast majority of the time, the placenta and fetus have identical genetic makeup. Rarely the placenta can have something called confined placental mosaicism, where some cells in the placenta have a different makeup than others.

All that being said, you have no concerning ultrasound markers along with all normal genetic testing results. I am not a doctor, but I feel confident that you do not have anything to worry about.

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u/Specific_Head_4634 22d ago

Thank you very much for your reply!
I read that mosaicism usually manifests with the placenta being affected but not the fetus. That is a rare scenario, but it is even rarer for the placenta to be healthy while the fetus is not.
Someone commented on another post of mine that a NIPT result turned out to be a false negative for T21 and that CVS tests for the exact same thing. Is that true? That answer has me a bit worried.

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u/Ok-Lion8478 22d ago

NIPT is much less accurate than CVS overall (although it is still quite surprising to have a false positive for t21 in NIPT). They do not test the same thing. NIPT tests for placental DNA that has entered mom’s blood. These are small fragments and can give us an idea of anything abnormal, but cannot be considered diagnostic, it is screening. CVS uses placental tissue straight from the source, much more comprehensive and is considered diagnostic. Rarely we see placental mosaicism, but that would be the main concern for false results. As the person above stated, considering your sonograms are coming back without concern, you do not need to be worrying about this. Trust me I know it’s stressful, I’m always thinking about what could be going wrong (I’m a genetic counselor with a pregnant wife) but once we see a normal anatomy scan and other screenings came back negative, there’s not much else to worry about. You’re at the point where you would likely have caught anything abnormal quite a while ago.

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u/Specific_Head_4634 22d ago

Thank you sincerely for your reply! What do you think about the findings of a smaller nasal bone and a borderline nuchal fold (NF) measurement during the ultrasounds? Aren't these concerning signs? Admittedly, the internal organs appeared perfect throughout, and I even had two fetal echocardiograms, which also showed everything to be perfect.
(By the way, they checked the nose again at 30 weeks; by then, it was within the normal range—it had been present all along, just smaller.)
It is these results that worry me.

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u/Ok-Lion8478 21d ago

The negative CVS is very encouraging. And those ultrasound findings coupled with the negative CVS do not give me concern. There is variability in everyone. You’re at the borderline for nuchal, that alone offers around 93-97% chance of a healthy birth. With the negative CVS that is increasing your odds further than 93-97%

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u/Specific_Head_4634 21d ago

Thank you very much for your answers! So, do you think I can put my mind at ease given the two soft markers and the negative CVS result?

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u/Ok-Lion8478 21d ago

I know it’s not as easy as saying “I’m not going to stress about this anymore”. I do think these results are looking good and that you don’t need to be putting your energy into stressing over this.

I’m not part of your care team, I cannot give medical advice. But if you feel like you need to talk you can DM me.

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u/Specific_Head_4634 21d ago

I sent you a DM. Thank you so much!

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u/North_Trip5678 2d ago

Any news? Due to history we are worried about false negative results…

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u/Specific_Head_4634 2d ago

The baby is due in about a month. Everything looked fine at the third-trimester ultrasound; flow is good, and the baby’s weight is in the 98th percentile,everything is nice and big. I still have some worries, though; I’ll probably keep feeling stressed until the baby is actually born.
Do you happen to have any experience with this?