Difference between NIPT and hospital blood tests?

[LBunz]

Hi. Sadly found out that I have a 1/89 chance of baby having Edwards or Pataus (MW didn't specify).

My inital reaction was to have the amniocentesis tests, because it can can give you a definitive diagnostic testing as opposed to the percentage / ratio likelihood with the bloodwork and I think the worry would tear me up if left to a 'possibly' outcome.

Can someone who has more knowledge of this tell me why the private bloodwork is more accurate? Not the science obviously but I'm struggling to understand the difference between the two sets of blood testing.

Money is insanely tight for us right now and unfortunately our trust doesn't offer this for free so I'm trying to weigh up options.

Thanks

Hi,

I had a 1:95 chance of Down syndrome. So we decided to go for the NIPT.

It came back as 1:100000 for DS and Edwards and 1:5 for Patau.

If I’m honest, in hindsight I wish I had just done the Amino. It’s caused stress and the waiting is horrendous. Also, when we got the results it was via an email on a Saturday afternoon. Nobody at my hospital or at the clinic was available for me to talk to. I’ve just cried buckets.

Today, I’ve had my Amino. Which is uncomfortable but by the end of the week we’ll know yes or no, and no more screenings or maybes!

I mean so many women have had amazing results for NIPT! But from my experience I wish I had skipped this step.

Xxxx

Thank you so much. My head is telling me just to go straight for the Amino even with the risks of it. I know that even if I had good results from the NIPT I would still be doubting in my head.

I hope the Amino results go well for you [flower]

The NHS test looks at 2 hormones in your blood (pappA and bHCG) that are likely to vary in the case of some of the trisomies, but can also vary for other reasons e.g. pappA can be linked to placenta issues. The NIPT takes advantage of the fact that some of the foetal DNA is in the pregnant woman's blood and basically looks at the mix of chromosomes. If the parent doesn't have a trisomy but there are too many copies of a particular chromosome in the mix then it is almost certainly from the foetus (similarly if there are y chromosomes in your blood you're carrying a boy!). So not perfect (because it's testing a mix of two people's blood) but a lot more direct as a measure of what is going on. Finally the amnio or CVS allows direct sampling of the foetus's DNA so is most accurate but carries a small risk of miscarrying a healthy pregnancy.

Antenatal results and choices (ARC) are really helpful for people in your position.

For what it's worth I had a risk of 1/52 of Edwards and similar for patau, NIPT gave a risk of 1/10,000 and DS is fine (though I did have pre-eclampsia which may be related to low pappA).

@UnaOfStormhold that was incredibly helpful. Thank you so much. I was trying to speak to the team at the hospital today about this but after waiting a total of about 2.5 hours as 'number 1' in the queue (over 3 calls) I gave up.

I had a 1 in 13 chance of downs syndrome. Decided to opt for NIPT but waiting 2 weeks for the results was horrendous. We had to fork out the money for it too and in the end I wished I'd just gone for the amnio. I had a really rocky pregnancy as I couldn't get the 1 in 13 number out of my head and wished I'd had the certainty of a negative test, rather than more possibilities (even though the NIPT is highly accurate).

@LBunz I'm sorry you're finding yourself here. It's awful to get High chance results.

Please bear in mind that although the NIPT says it's highly accurate, it's not diagnostic. It's actually less accurate for T13 and T18 where as for T21 it's very accurate.

If you were to decide to end the pregnancy with a diagnosis of a chromosomal abnormality, I would recommend going for a CVS or amnio, depending on how far you are in your pregnancy.
Due to the NIPT not being diagnostic, your hospital would need to do to a amino or a cvs to confirm the NIPT results.

^^ This.

If the NIPT comes back as high risk you will need the amnio or CVS test anyway.

If NIPT comes back low risk, you won't be offered them. Remember though that the NIPT gives you a percentage likelihood, whereas amnio/CVS give you a definite yes or no.

The downside of amnio/CVS is they are more invasive and come with a small risk of miscarriage.

Ask to discuss further with your midwife if you've got lots of questions. Both tests can be done at any time during the pregnancy so you don't have to decide imminently, you have time to do some research

Hey not sure if you’ve moved forward this, but I was high risk for Edwards and Pataus. The combined screening measures blood serum which is an indicator of pregnancy growth hormones (HCG and PAPP-A) which can indicate issues.

The NIPT measures cell free DNA which they hope comes from/is representative of baby/placenta. Unfortunately whilst the detection rate is high, it vastly over-represents a lot of conditions. Or there can be confusion between maternal and fetal DNA. This is why it only accurately predicts Edwards in roughly 37% of cases (37% PPV). There are a LOT of false positives. It is basically suited as a Downs Screening as it can be 80% accurate.

I would second that unless your concern is Downs, it is worth going straight for amniocentesis. The amount of stress a false positive NIPT screening can provide is truly heart-wrenching. Especially as most people believe the test to be so accurate.

Negative results from NIPT can be very accurate. Hence many people who have had a negative result love this test and feel reassured. However the pendulum can swing the other way.