Should I believe NIPT test or scan?

[58ESY58]

So I had an NIPT test done at 14+1 weeks with fetal fraction of 18%. The gender came back as female but just had my 20 week scan and the sonographer was positive it was definitely a boy - and from what he was explaining on the screen, it does look like a boy.

Just not sure which to believe? I’ve read that NIPT are more accurate than scans when it comes to gender. NIPT tests are meant to be >99.9% accurate, and because fetal fraction was high and I didn’t have the test done too early, I’m wondering how it could’ve been wrong? Which do I believe?

And I am also wondering, if the NIPT test is wrong about the gender, could it be wrong about chromosome abnormalities? That’s what we initially did the test for, to see if there are any abnormalities. It came back low risk for everything but now I’m doubting the test altogether. Should I be worried?

NIPT does tend to be accurate but where the NIPT and an ultrasound differ, especially if the scan was clear, ultrasound is usually correct- this is what we were told anyway.

I mean if there's a visible penis on the scan, I'd be inclined to guess that it will still be there when the baby is born...

Someone has to be in that 0.1%!

You could always get a private scan in a few weeks and ask them to confirm the sex, if you want a second opinion to back up the NHS sonographer.

Also, and I hesitated to post this, you might want to check that there are no issues with a DSD. I have previously read a study which said that in instances where NIPT and observed sex does not correlate, it can sometimes be because of a DSD. I think additional tests can be done on the NIPT sample to find this out? I am not an expert in this at all, but you might want to ask.

Sorry to scare you, but if it was me I would rather know prior to/at birth, rather than not finding out until the child reaches puberty.

Hope it's just an NIPT error.

Neither are diagnostic tests so you can't really trust either 100%.

NIPT are very accurate, especially after 10 weeks - but like all tests, can be wrong for a very low percentage, no reason you can't be in that. With NIPT if you've got a boy on board, the Y DNA should be present and at 14 weeks I'd certainly think it would be.

Can you go and have a private scan, that might put your mind at ease one way or another.

I'd probably just go and get another private scan, specifically to look for the sex, if I didn't want to wait and find out at birth.

I'd also raise it at the next midwife appointment, as you mentioned the screening aspect of it. I'm not sure on whether accuracy of sex is linked to accuracy of screening, but this is something your midwife should be able to advise on.