r/genetics • u/Specific_Head_4634 • 2d ago

Article False 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.

1 Upvotes

60% Upvoted

17 comments sorted by

15

u/BoopBaDoop420 2d ago

False negative on CVS is very rare. The concern with CVS is a false positive due to confined placental mosaicism, where the placenta is abnormal and the fetus is not. It’s a rare occurrence for the placenta to be normal and the fetus abnormal.

2

u/drewdrewmd 1d ago

False negatives for the things tested for are rare. There are many things not tested for that could cause mild dysmorphisms like this.

1

u/Specific_Head_4634 18h ago

What exactly are you referring to here?

1

u/drewdrewmd 17h ago

I mean whatever testing they did on CVS is mainly for chromosomal disorders, presumably not whole genome sequencing, single gene stuff etc. There are also many congenital anomalies and syndromes that do not have a genetic basis. Even people who have had good counselling don’t usually really understand what’s being ruled out.

1

u/Specific_Head_4634 17h ago

I see! Actually, I wasn't even offered a WES test... they said those are associated with higher NT values.

1

u/Valik93 1d ago

With a negative KT, FISH, Array, and only a smaller nasal bone on ultrasound? You can never really exclude 100% a genetic abnormality no matter what test you use, but chances are overwhelmingly in favor of everything being ok.

0

u/Specific_Head_4634 18h ago

Yes, KT, Fish, snp array negative. The NT value was still within the limit and smaller nasal bone. What is your take on this?

1

u/Valik93 18h ago

Same as before. I don't expect any chromosomal abnormality.

I understand that the NT value was very close to the limit, which is why you were tested. But if we're super strict on indications, your pregnancy is not even considered at risk with only 1 minor sign on ultrasound. So try to relax and enjoy what's left of the pregnancy. Once the child is born, your number of sleep hours will be reduced drastically.

1

u/Specific_Head_4634 18h ago

Also, there were two negative fetal heart ultrasound results; I left that out.

0

u/Specific_Head_4634 18h ago

Thank you very much for your reply! May I ask if you have any experience with this?
Could I perhaps send you a dm?

1

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u/One-Treat4655 2d ago

Nah. NT and nasal bone are historic relics. Just do cell free dna. Your baby is fine.