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Reader Q&A: The new MaterniT21 screening test for Down Syndrome

Tracy G. writes in today with a question on a new screening test:

I have the most recent version of Expecting 411. There’s no mention of the new MaterniT21 test and I wondered if you might address it on your website? Would really love your take on it as I have come to trust your guide for all matters re:pregnancy. I just got a negative result from the MaterniT21. I am hoping to arrive at a decision about whether to “go to the bank” with this result or to have an amnio.

Dr. H responds:

Congratulations on your pregnancy and we are so happy you like our book!

The MaterniT21 test, which is the brand name for the Sequenom free fetal DNA test (there’s also a version by Verinata) can screen for fetal DNA in mom’s blood and assess trisomy 13, trisomy 18 and trisomy 21 (Down syndrome) risk with 96-99% sensitivity.  Over, it is probably a better screening test than what we currently use as standard, but it was just approved in February and most offices aren’t offering it to all patients.  In fact, it is specifically for high-risk pregnancies, and is not currently used in low-risk patients.

The fact that yours is negative is fantastic and at this point, assuming your nuchal lucency (the ultrasound looking at the thickness of the baby’s neck) was negative as well, you could choose to skip a CVS (chorionic villus sampling) or an amniocentesis.  I always remind patients, however, that all of these tests we are discussing (the first trimester test, the MaterniT21) are screening tests.  And although they are very good at detecting babies with chromosomal problems, they are not perfect.  The only way to know for sure, is to do invasive testing via a CVS or amnio.  Now, that being said, if you and your practitioner are happy with your screening test and the probabilities given to you, it would be perfectly reasonable not to go ahead with invasive testing.

Good luck with the remainder of your pregnancy!

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