Genetic testing usually happens late in the first trimester, so around 11 to 13 weeks. We offer a few different tests. One of them is called the first look. It's based on the idea that babies that have Down syndrome have a thickened fold behind their neck.
The first thing we do is an ultrasound and the purpose of that ultrasound is to look for that fold behind the baby's neck. The second thing is that babies who have Downs tend to have moms with certain chemical markers that are higher or lower than in moms that don't carry a baby with Downs.
The second part of this is testing those chemical markers. We put the ultrasound results along with those markers into an algorithm and come back and say your risk of Downs. We may say the risk of Downs is 1 in 10,000. That's really low and there’s probably nothing else to do or we might say the risk of Downs is 1 and 3. If that's so, then we need to do additional testing because this is just a screen.
The other form of genetic testing that you may be offered is called non-invasive prenatal screening and there are lots of brand names that go with this. You might have heard of Maternity 21, Panorama, or Harmony. It's all a type of non-invasive prenatal screening that's based on the idea that the baby, actually the placenta, sheds cells into moms blood supply.
With just a blood draw, you can figure out if the baby has some of the most common chromosomal disorders. Down syndrome is one we know. It also looks at trisomy 13 and 18. People tend to like it because it will tell you the gender.
How do you decide whether you want to get this test or not?
I think that there are three groups of people. Group one would say if the baby had a serious chromosomal disorder, I may consider ending the pregnancy. That group should definitely get the test. Group two would say I wouldn't end the pregnancy, but I would want to know so I could emotionally prepare to take care of a child that may have special needs.
That group should get the test. Group three would say it's not going to change anything. I wouldn't end the pregnancy and I don't need to know to emotionally prepare. What will be will be. I would not get an amniocentesis anyway. It's important to remember that when we do this genetic testing in the first trimester, it's just a screening test.
You actually need to do an amniocentesis where we take a very thin needle, stick it into the belly, into the uterus, and into the fluid around the baby, and send that off. That gives us the best answer in terms of what's going on with the baby. I give the example of a patient that I had many years ago who had a positive screen for Downs. Her risk was 1 in 74 and she was terrified. She didn't want to get an amniocentesis, so she spent the entire pregnancy being horrified that her baby might have Downs.
I kept saying, “the chances are greater than not that the baby doesn’t,” and that was not of comfort to her. I think it's really important to think about how am I going to use this information. If you're not going to get the confirmation with an amniocentesis, then it's probably not worth doing this screening test in the first place.
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