Advantages of Pre-natal Nuchal Translucency Ultrasound v. Blood Test?

August 7, 2015 7:11 AM

Hello! I can't seem to find the answer to this on the internets, so while you are obviously not my doctor, I'd love some advice. Is there any benefit to having the nuchal translucency screening v. the fetal DNA blood test (MaterniT21)?

I am 11 weeks pregnant. I recently moved to a place that doesn't generally do the Nuchal Translucency Screening test (ultrasound and blood test) on national health care. I had one for my last pregnancy, so I find this a bit odd. I'm also thinking about getting the MaterniT21 test (like the Harmony fetal blood DNA test. (I'm over 35). I'll have to pay for either both or either of these. Is there any benefit to getting both, or is that just overkill?

TLDR: Does anyone know if the NCT screen does anything more than the MaterniT21 screen? Is it worth paying for both?

Thanks!

posted by anonymous to Health & Fitness (10 answers total)

We asked this same question of our midwives, and are roughly in the same boat as you. We had our first kid 3 years ago, before the MT21 test and had the NCT done. The MT21 screen is much, much more accurate and zero risk, so if it comes back clean you're all set. If there's any doubt, then they'll do the NCT.
posted by Oktober at 7:30 AM on August 7, 2015 [3 favorites]

If it matters to you, I believe the MT21 test can also reveal gender much earlier than the standard anatomy scan. The NT test cannot.
posted by peanut_mcgillicuty at 7:35 AM on August 7, 2015

This previous question had some excellent links. I am not your GC or your OB but the quick answer is that the NIPT and NT sono use different methods to assess the chances of overlapping but different ranging fetal issues. Neither is diagnostic, both have false positive and false negatives and invasive testing such as amnio or CVS should be performed if diagnostic/actionable levels of information are needed. NIPT uses fetal DNA in the maternal system to assess for select chromosome conditions; it does not assess for all chromosome abnormalities and is well known to not be diagnostic, especially for T13 and microdeletions. NIPT does not assess for fetal physical anomalies at all, any concurrent physical condition is likely due to a chromosome anomaly if detected. Assessment for T21 and T18 are more accurate but still have false positive/false negatives. The NT scan assesses the fetal physical status, specifically the NT region but other areas are looked at as well, and so may assess an increased risk for non-chromosomal conditions such an neural tube defects, etc. If a fetal anomaly such as an increased NT is seen, other testing is needed to determine information as to the cause.

Overall, depending on your desire for diagnostic actionable level information, you may want to skip either and proceed directly to CVS/amnio. If you're not looking for actionable level info and would not consider CVS/amnio, you may want to skip both in deference of songrams later in pregnancy.
posted by beaning at 7:54 AM on August 7, 2015 [1 favorite]

FWIW I had both (Harmony) and my insurance covered both for both of my pregnancies. Since insurance companies don't cover duplicate tests for no reason, presumably there are statically significant benefits to both. From what I could tell from reading online, the main benefit to NCT is the ultrasound since it can detect physical abnormalities. The MT21 test is more accurate for detecting what it tests for, but since it's only a blood test it doesn't pick up things it doesn't test for, like rarer chromosomal issues that might be noticeable in an NCT ultrasound.
posted by gatorae at 8:04 AM on August 7, 2015

This answer from Dr. treehorn+bunny from a similar Recent Ask is the one you are looking for.

tl;dr Feel free to skip the NT entirely in favor of doing cell-free fetal DNA testing such as MaterniT21.
posted by hush at 8:28 AM on August 7, 2015

This, according to my own experience of these tests and the info consistently given me by several OBs (I had to switch around a bunch during early pregnancy): The NIPT test is much more accurate and is performed earlier. There are very very few false negatives, some false positives (but fewer than the quad screening). There are some complications that can make the test inconclusive, but they are uncommon and the MaterniT21 brand is, from my understanding, the best of the competitive tests. The out-of-pocket cost to me came to $75, I was told the max they would charge would be $300.

Was also told that the NT test is not necessary after the MaterniT21 test is performed. The only additional screening before the 20 week anatomy scan I did was the 2nd trimester blood test because there is one additional (rare) thing it screens for that is not captured by either the NIPT or the fetal anatomy scan.

I disagree with any suggestion to go directly to CVS or amnio. The false negatives for the MaterniT21 for chromosomal disorders are very low. The diagnostic tests can be performed if there is any evidence of issues, but they carry a risk of miscarriage.
posted by vunder at 9:28 AM on August 7, 2015 [2 favorites]

Yeah the NT test is way less accurate at detecting t21 and doesn't check for t13 and t18. Fwiw an early ultrasound could detect a whole boatload of other physical anomlies. Waiting until 20-22 weeks to find out about major physical anomolies is dumb imho. I think they wait for resolution but at 16 weeks they can see a lot and you've spent way less time picturing your baby kicking you with a foot they may not have. I'd pay for maternity 21 and 1-2 first trimester ultrasounds if I had another. NT test is a vague sketchy marker thing that could flag t21 or miss it and flags lots of healthy babies. But if it made my ob agree to an early ultrasound I'd do it.
posted by Kalmya at 3:38 PM on August 7, 2015

Ok to clarify I didn't mean first trimester for ultrasounds. I really mean if I could just order up any medical testing I wanted for my unborn child as not medical doctor:

Ultrasounds at 6,11,16,22, and 36 weeks.
posted by Kalmya at 3:48 PM on August 7, 2015

I've known a couple of people who have gotten both and told me they just liked having the excuse to see their baby on ultrasound again.

I don't recommend that approach, because the tests are looking for the same problem (only the Harmony test is much more accurate), but if you get an abnormal NT scan you're going to be in an awkward position in terms of potentially wanting or having recommended a more invasive test like amniocentesis, even if your Harmony test is negative.
posted by treehorn+bunny at 10:48 PM on August 7, 2015 [1 favorite]

Beaning has got it. What are you going to do with the info? If you would keep the pregnancy anyway, no need to do any of these tests. If you think there's a possibility that you wouldn't keep the pregnancy, best to get the most accurate test you can.
posted by vignettist at 9:19 AM on August 8, 2015