I think the detection rates are significantly different. Your link shows that for trisomy 18 there's a 3% false negative rate with the Harmony test. I think the false negative rates are significantly lower for CVS.

CVS is indeed very accurate (97.5-99.6%[1]), but still has a false positive rate of ~1%[2]. But as you noted, CVS has a small risk of miscarriage, and for that reason many couples wouldn't even consider it.

Of course I can't speak for everyone, but I would guess that for most couples the biggest concern is T21 (it is the most common of the three), and the NIPT test is 99% accurate for that. Balancing the risks, and false positive and negative chances of NIPT vs CVS, NIPT seems more valuable to me.

[1] https://patient.info/doctor/chorionic-villus-sampling-pro [2] Mayo Clinic Complete Book of Pregnancy & Baby’s First Year. Johnson, Robert V., M.D., et al, Ch. 11.

Thanks. Are there figures for the false negative rate? I was struggling to find those.

It's certainly a reasonable option, but the context of the original comment saying that the parent would have known (or had the option to know) that the child had T18.

I didn't find false negative figures specifically mentioned as such for CVS or NIPT, only accuracy and false positive. I've assumed false negative == 100 - accuracy, but in reality results might also sometimes be "uncertain", which wouldn't count towards the false negative rate.