@MilsCookie the NHS test is basically a good guess. The nipt actually tests the DNA from your baby giving it a far more accurate result. The NHS test is 79 percent accurate for down sydrome. The nipt is 99 percent. The NHS test just uses your age and nucal results then puts that into a computer and it guestimates a number.
It really depends on whether you would continue with the pregnancy if your baby had down sydrome. The other two things they screen for, Edwards and Pataus are kind of irrelevant to the test to be honest as they are not conditions that are compatible with life.
That is why the Harmony/nipt has had some contravercy. Sally Philipps did a program on the test called 'a world without down sydrome'. Her son has down sydrome.
The NHS were actually supposed to be adopting the nipt anyway and rolling it out soon instead, so it was going to replace the combined screening anyway. But imagine now with covid that won't happen for a few years yet.
The reason people have it early is so they can terminate earlier then 20 weeks. Harsh to write it down like that but that is a big reason. Especially for women like us who have had miscarriages. The NHS screenings can come back in 24 hours like mine did, or they can take weeks. Then by the time you have amio or CVS to confirm the condition your very far along to go through a tfmr (termination for medical reasons).
It is very very personal and is bloody expensive. I've never had it before with my other two girls but I could absolutely not risk having a baby with a cromasonal condition, it would impact on my other children so much. My partners uncle had down sydrome and like everything even that condition is on a spectrum.
Sally Philipps son is very high functioning and my uncle in law was very low functioning with a multitude of other health conditions that are associated with down sydrome.
It's very rare but with statistics like 79% on the NHS test, I knew mine would be low risk (they were) because of my age skewing the results. So I could still either go on to find out the baby had one of the three conditions at the 20 week scan, or end up actually having a baby with down sydrome.
It was too much of a risk for me personally with a twin pregnancy especially.
I hope that makes it's clearer. I think alot of women think the NHS test is diagnostic which it totally is not. I could guess just by looking at a lot of women and still have a similar accuracy.
It's the 20 week scan that will usually pick up what the combined screening has missed. And that is just too late for a lot of women to consider having to then have further testing perhaps leading to termination