How to understand pre-natal testing

I'm Lisa Birnbach for howdini.com. These days, pregnant couples are faced with a lot more choices than what to name the baby and how to decorate the nursery. You're faced with amniocentesis and a whole array of other prenatal tests. How do you decide which tests you really want or need? We're here with Dr. Keith Eddleman, director of obstetrics at Mount Sinai Hospital in New York City, and author of two books on pregnancy, including Pregnancy for Dummies. Thank you for joining us, Dr. Eddleman.

Thanks for having me.

There's all kinds of screening. How do you start the whole process, and who do you rely on to guide you through it?

Well, it can get very confusing. These days there are a lot of different tests. And, really, your doctor will guide you through things. But basically, there are tests that everybody goes through, things like screening for diabetes, and doing an ultrasound to check for structural abnormalities or birth defects. And then there's things that people go through based on their personal history, their family history, or their ethnic background. And those are things that your doctor is going to ask you at your first prenatal visit, to help you decide which tests are right for you.

My husband and I had to wait in a room at Mount Sinai Hospital to take something called the Tay-Sachs test, because of our ethnic heritage.

You probably underwent genetic counseling, where they do a pedigree. They went back three generations of your family. And what they're doing is they're looking to find out if there are patterns in your family that might indicate something that's genetic that you might not be aware of. In fact, most people aren't. So that's the purpose in doing that. And the Tay-Sachs was done based on screening for people from a Jewish background. And there are multiple tests that are done in people of Jewish ethnicity. There are tests that are done for people that are African American, Asian, and so forth.

Is there a test for everybody, or are there some Anglo-Saxons who don't need testing?

Well, it's recommended that all couples be made aware of testing for cystic fibrosis, which is a disorder that's most common in people of northern European ethnicity, but it's prevalent, really, throughout the whole world. So it's recommended that they all be at least made aware of the availability of the testing. The other thing that everybody should get is a screen for diabetes. Everybody should get that. And then probably the third thing is I think that everybody should have an ultrasound to check for fetal anomalies or birth defects.

Now how many of the tests that we're supposed to take are blood-based tests?

Well, the testing now that's recommended for chromosomal screening, like down syndrome, we recommend that you to do that in the first trimester. And that's a combination of a blood test and an ultrasound. And that will help you determine whether or not you're at an increased risk for a chromosomal abnormality, say, like down syndrome. And then the blood test for diabetes is a blood test, if you will. The blood test, or the testing, for Tay-Sachs disease is also a blood test.

Sickle cell anemia.

Sickle cell anemia is a blood test.

Cystic fibrosis?

Is also a blood test. They're genetic tests. And then the routine testing that you have done at your prenatal visit that determines, say, your blood type, and your hematocrit, and whether or not you're anemic, things like that. Those are blood tests, also. So, really, the majority of them involve some blood component. They might also involve an ultrasound component, too, but most of them are blood-based.

What about the genetic stuff? Does age have anything to do with that?

After age 30, the chances of chromosome abnormality start to creep up.

Yeah, if you look at charts, it's shocking.

It is.

30 is one thing, and then 40, you might as well just go home.

Well, 35, it really takes a sharp increase, and it really dramatically increases. So that by 40, 45, the risk for chromosomal abnormalities are significant.

Does that mean that, basically, every woman who is getting good prenatal care at the age of 30 or 31, or-- is there a number, an age, at which she will be advised to have amniocentesis?

It used to be that women at the age of 35 routinely had an amnio. And at that age, their risk for chromosomal abnormality was about 1 in 250. So that's the risks at which you should think about doing what we call a diagnostic test, which is CVS or amnio. But some women now, even at 1 in 250, don't want to do that. And then some women who even have a risk of 1 in 10,000, which is really low, still want to make sure, and still want to do the invasive tests. So really it's a personal decision, and your doctor will help you make it.

OK, great. Thanks so much, doctor. For howdini.com, I'm Lisa Birnbach.