Why is there prenatal testing for Down syndrome?

T21 CellAt my very first national medical conference, I received an answer to the question: why is there prenatal testing for Down syndrome? I have shared the response I received in many presentations. At last week’s ACMG conference, I learned of another reason. It struck me as profound. I wonder what you think about it. 

In 2008, I attended the Annual Clinical Meeting for the American Congress of Obstetricians & Gynecologists (ACOG). This was my first exposure to a professional medical organization’s annual meeting. I was in awe of the exhibit hall.

I was there exhibiting with representatives from the National Down Syndrome Congress and the National Down Syndrome Society, along with members of the local Down syndrome support organization, the Down Syndrome Association of Greater New Orleans. We were placed on one of the exterior rows of exhibitors, in the smallest exhibit space available. In the center were huge architectural structures for genetic testing laboratories and pharmaceutical companies, all marketing their services and latest products.

At that time, the newest prenatal testing technology was combined testing. Combined testing combines nuchal translucency, an ultrasound measurement of the fetus’ neck, with the test results of the mother’s blood. Even though it would be three years before its test for Down syndrome actually made it to market, Sequenom was at the conference. Sequenom was marketing its prenatal test for Rh-incompatibility, and reporting the latest results on its non-invasive prenatal test for Down syndrome.

As at every conference I attend, I visit with the various exhibitors to understand their industry, products, and perspective. After talking to several laboratories about their various services for prenatal testing for Down syndrome, I found my way to the Sequenom booth to ask the fundamental question:

Why is it Down syndrome that is the condition prenatally tested for?

The basis for my question was that I had received the glossy folders from other laboratories that list the dozens of other genetic conditions that can be tested for prenatally. Why is it that Down syndrome is the subject of prenatal testing? The simplicity of the answer was sublime.

The representative at the Sequenom booth explained

“All you have to do is count.”

She further explained, “once you’ve counted past 46 chromosomes, you know you’ve found a Trisomy.” That is why Down syndrome is the subject of prenatal testing: it’s easy. Down syndrome stands out even at the genetic level.

But, at the ACMG conference, another presenter explained how Down syndrome also stands out at the prenatal level.

She explained that Down syndrome was the subject of prenatal testing because, in her words, “the fetus looked like a person with Down syndrome.” She described how the thickness at the back of neck that is seen in some individuals with Down syndrome was the insight for the first trimester nuchal translucency test. Her remarks made me flashback to a maternal fetal medicine (“MFM”) specialist I spoke with in 2008.

Image of a nuchal translucency test.

Image of a nuchal translucency test.

This was at my very first poster presentation. It was held in Montreal as a joint meeting with ACOG, the Royal College of Obstetricians & Gynaecologists (RCOG), and the Society of Obstetricians & Gynaecologists of Canada (SGOC). This MFM was from Atlanta. He talked about how he could detect almost every fetus with Down syndrome prenatally based solely on an ultrasound.

The MFM described how he would measure the nasal bone, the long bones of the limbs, and the pinky finger. This is because in individuals with Down syndrome common physical characteristics are a flat bridge of the nose, short limbs, and a small pinky finger. All of these measurements of the fetus are considered “soft markers.” And though I had read about them for years, and heard them described five years ago while standing in front of that poster in Montreal, it wasn’t until I heard the poster presenter’s remarks at last week’s ACMG that I about fell over:

“The fetus looked like a person with Down syndrome.”

So five years after hearing how Down syndrome stands out even at a genetic level, by having a 47th Chromosome, I appreciated how individuals with Down syndrome stand out physically, not just in general society, but even in the womb.

And, so, this is why there is prenatal testing for Down syndrome from a purely practical standpoint: Down syndrome was one of the first conditions tested for with amniocentesis at the dawn of prenatal testing because all it took was for the lab tech to count past 46 Chromosomes. In the newer age of prenatal screening testing, Down syndrome again is the subject of testing simply because you can look at an ultrasound and see a person with Down syndrome.

I find this statement incredibly profound. I wonder if you do, too. What meaning is in the statement, “the fetus looks like a person with Down syndrome?”


  1. The fetus looks like a person with Down Syndrome. Hmmm. I thought the whole position of pro-sbortionists was that a fetus wasn’t a person. So how can a fetus look like a person with Down Syndrome? Either it’s a person or a fetus. If its a person then abortion is murder. Only people can have Syndromes. Fetus’ cannot.

  2. Beth Biller says:

    I think it means you have an extra special little one that will love you unconditionally forever. While they will need closer chaperone, there will be no other to love you as much. Beulah will always have a greeter and one to keep the line moving quickly.

  3. Thank you both for your comments. I just wonder if those who made the realization that because a fetus with Down syndrome looks like a person with Down syndrome, and therefore distinguishing physical characteristics can be identified prenatally through ultrasound, if that realization made them reconsider what exactly they were looking at when taking those ultrasound measurements.

  4. Thanks Mark. The statement makes it obvious. “A person’s a person, no matter how small” Dr. Suess has a deeper meaning now 🙂

  5. Matt "Pitts savior" Lytle says:

    Mark Leach- find a better cause to support. Information to make educated decisions should not be questioned.

    • You obviously haven’t read this post or any of the other hundreds posts here if you think I’m against women making informed decisions. As written extensively on this blog, however, the way prenatal testing is administered too often does not result in informed decisions being made, but rather the imposition of ignorant, bigoted, outdated, and unsupported advise and counsel about prenatal testing and the conditions tested for.

  6. Shelley Lampe says:

    Thank you for this thoughtful post Mark. It is so very very sad to me; where has the humanity of humans gone? The answer to the question is simple. Man no longer sees people as beings created by God in His image, rather, they are seen as merely animals, composed of a set of characteristics and attributes. People with “defects” are just that, defective. And since most people view children as possessions, who wants to have a Corolla when you can have a Lexus? Who wants a saltine when there are artisan breads at the table? So there is prenatal testing for DS because it’s not only okay, but acceptable, educated, and “responsible” now to say “I don’t want a defective child.” Lastly, there is money to be made indulging that barbarian mentality, which means it’s here to stay. May God have mercy on us.

    • I think studies have shown that the perception of a Corolla or a saltine as an inferior product may be just the car or cracker meant for them.

      • Shelley Lampe says:

        🙂 (Seriously though, I’m kind of a Corolla and Saltine kind of girl…which maybe is why I am also a one-of-my-children-has-DS-and-I-love-her-like-my-other-children girl too.) Thanks for all your insight Mark.


  1. […] syndrome is a shortened pinky finger, which may curve inward, termed clinodactyly. This is a “soft marker” because such a finding by ultrasound is not definitive for any chromosomal condition, but […]

  2. […] (great read- Why is there Prenatal Testing for Down Syndrome) […]

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