What is the clinical utility of Down syndrome prenatal testing?

SMFM logo imageYesterday’s post on the Society for Maternal-Fetal Medicine’s statement saying noninvasive prenatal screening isn’t ready for the general population left out a significant sentence. It raises the question: what is the clinical utility of Down syndrome prenatal testing?

As covered in yesterday’s post, SMFM issued a statement in response to the New England Journal of Medicine study associated with NIPS lab Illumina suggesting NIPS was ready for the general population. SMFM had a litany of reasons to demonstrate that, no, NIPS is not ready for the general population. But I left out one of the stated reasons and it deserves our focused attention.

In the paragraph explaining the many limitations of the Illumina study, I missed the significance of this sentence when I did my first hasty read. But, in re-reading the statement to draft yesterday’s post, the sentence leapt off the page at me.

Another reason SMFM says the Illumina study does not support offering NIPS to the general population is because:

A high percentage of the samples for NIPT were collected in the third trimester – at gestational ages when clinical aneuploidy screening is not performed and is not clinically relevant, yet when fetal DNA amounts are far higher allowing better test performance.

Did you catch it? The phrase that deserves examination?

Let me first bracket off the part that is non-controversial. SMFM is right to note as a limitation of the Illumnia study that a high percentage of the samples were collected in the third trimester. At that stage of the pregnancy, there is more DNA from the pregnancy than at any other time in the mother’s bloodstream allowing for NIPS to perform better, but the minority of women undergoing NIPS testing will be waiting to do so in the 3d trimester. Including these results, therefore, skews the Illumina findings, since they are not representative of how women in the general population would undergo NIPS test.

Okay, so that’s fine. But note the remaining part of SMFM’s critique of including third trimester NIPS results:

when clinical aneuploidy screening …is not clinically relevant

I think here is a moment where the veil slips revealing a long suspected, but rarely explicitly stated, view of the clinical utility of prenatal testing for Down syndrome and other aneuploidies.

Why is returning test results in the third trimester not “clinically relevant?” Isn’t prenatal testing all about respecting a woman’s right to get information about her pregnancy? If NIPS testing is more accurate than ever in the 3d trimester, then shouldn’t that be a good thing for an expectant mother to know when considering prenatal testing? She could wait until after the 2nd trimester, when bonding typically occurs, and then find out before giving birth so she could prepare herself, her loved ones, and, depending on any health issues, her birth plan for her expectant child. How is that not “clinically relevant?”

I think you know why.

That one phrase reveals what SMFM, and by association the medical profession, thinks is the clinical use for prenatal testing:

Prenatal testing is not for providing a woman information so she can prepare for the birth of her child.
Prenatal testing for Down syndrome is clinically relevant when it delivers results in time for the mother to abort her child.

That is the only difference between results delivered before the 3d trimester and then in the 3d trimester. The information remains the same, the only difference is whether it is actionable. With most states banning abortion in the 3d trimester except when the mother’s life is in jeopardy, that is why SMFM draws the line for when prenatal testing for Down syndrome is clinically relevant: clinical meaning when you can prevent the birth of the child through abortion.

This puts the lie to the oft-stated defense I have heard from practitioners, lab representatives, and attendees at medical conferences when the ethics of prenatal testing for Down syndrome are discussed. They are quick to defend against the eugenic critique that the only purpose of prenatal testing is to allow for abortion by saying, “well it also provides value because it gives women information so they can prepare for the birth of their child.” I actually agree with that point because it is one that many women who had a prenatal diagnosis have shared with me. But, from a strictly clinical perspective, SMFM has made it clear in that simple phrase in its recent statement:

Clinically, prenatal testing for Down syndrome is relevant when it can allow for abortion of the child.


  1. That’s the crux of the issue, and the only reason any national screening programme is funded by the state.

  2. The whole thing makes me sick to my stomach. I have two sons, my youngest has DS and I refused testing from the 12-14 week CVS to the 20 week amino as I was not going to get rid of him. He is the perfect addition to our family…

  3. If you have the opportunity to prevent a life which will never be able to take for granted what those of us without disabilities do, then why wouldn’t you? DS is associated with serious life-limiting illnesses including leukaemia and cardiac diseases; those with DS rely on others’ consistent advocacy. Look around and witness how the human species regards and treats those who cannot self-advocate, then wonder how you could consciously be responsible for bringing someone into this world who will always rely on others’ kindness. Please research into abuse of the disabled and elderly.

    • The human condition is associated with life-limiting illnesses including leukemia and cardiac disease. We all rely on other’s consistent advocacy and rely on other’s kindness. But even if you are saying that those with DS rely moreso because of developmental delay associated with DS, then by your logic lives should be ended that become disabled. Rather, including, preserving, welcoming those differently abled make us kinder, since they rely on that kindness. And eliminating those who rely on our kindness make us less compassionate and caring.

      That said, do you have a relationship with someone with DS?

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