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Diagnostic Tests


All right. So now let’s talk about diagnostic tests for a minute. We’ve been talking about how ultrasound is a screening test. Let’s talk about how would we know for sure if a baby’s chromosomes are abnormal. I mentioned one diagnostic test, or one “yes or no” test. I mentioned amniocentesis. It’s one of them; it’s the most common diagnostic test that we do. And the second most common diagnostic test we do is called chorionic villus sampling. And I’ll talk to you about what those are. So an amniocentesis has a risk of causing a miscarriage, I mentioned about one in 270. If you do lots of them, it’s a lot less than that. There are some big studies now that show the risk is probably as low as one in 1500. So, less than one in a 1000 chances of causing a miscarriage by doing the test. But if you do fewer of them it may be as high as one in 200. So the risk is somewhere between one in 200 and one in 1500 of causing a miscarriage. Now you might think “why would an amniocentesis cause a miscarriage?” A lot of people are really thinking, “Oh, it’s because you poke the baby with the needle.” It’s not that so much as it is that if you did something that caused mom to deliver the baby, and if you’re 20 weeks along, the baby’s not going to survive that. So it’s things that could cause a delivery. Things like an infection or causing labor. Those are the kinds of things, causing ruptured membranes and then moms getting an infection and going into labor. Those are the kinds of things that would cause the problem. Now you can do an amniocentesis as early as 15 weeks. If you do it before that, it increases the risk. And you can do it later. You can do it all the way up until the time the baby’s born. Okay?

Now let’s talk about the other test ... chorionic villus sampling. This time the target, rather than amniotic fluid, is the placenta. Okay. So what we typically do is look with a speculum like we were going to be doing a pap smear and then the doctor will clean off the cervix and slip a little catheter up into the cervix and, using ultrasound, guide the catheter into the placenta and basically take out a little piece of placenta. Okay. And then that piece of placenta can be put in a culture dish and for a week or two grown and so then you could take the cells from the placenta that came from the baby and then you could look under the microscope, make a karyotype out of them and then count the chromosomes. Okay. That’s the same way with an amniocentesis only with an amniocentesis we’re just taking the amniotic fluid and in the amniotic fluid there’s cells that came from the baby’s skin. So we just grow those cells for a couple of weeks and that’s how we can tell the chromosomes, okay.

Now back to chorionic villus sampling. This test is a little bit different than an amnio in that it can be done earlier. In fact, it usually has to be done earlier. It could be done as early as in the 12 to 14 week timeframe. Okay. So that’s its primary benefit. Its biggest downside is that it tends to be associated with higher risk of miscarriage. And this is a test that it really makes a difference in how many you do. So if you do lots and lots of them, the miscarriage rate is probably as low as the amnio miscarriage rate, or even lower in some people’s hands. But the average person tends to have a higher rate of miscarriage with CVS than they do with amnio. And if you don’t do very many, it can be as high as 10 percent. Okay. So there are a lot of institutions in the military and out of the military, smaller places, even some of the big medical centers that don’t do CVS because we don’t do lots of them. I don’t do that. I do lots of amnios because I do them, but I don’t do CVS because I don’t do enough. Okay. But if you needed CVS, then we can send you, we can refer you to a place that does CVS. Okay? All of that is a little scary isn’t it? Talking about invasive procedures but those are the “yes or no” ones.

Now let’s talk for a minute about another way we can try to look into the womb without having to put needles in there. All right. We’ll look at some other non-invasive tests. And there’s a lot of new stuff that’s come out and it’s gotten really complicated because there’s a lot of new stuff. There are tests now that can be done in the first trimester. There are tests that we do in the second trimester. There are tests that we do as combination of the first and second trimester. There are serial, combined, contingency, integrated, fully-integrated. It’s gotten complicated. These tests involve the use of maternal blood to test for baby’s issues, and some of these tests are actually combinations of blood and ultrasound together. Okay. So we’ll talk about those and in the end we’ll talk a little bit about a strategy that you can pick to help you screen for, if you choose to do screening. And we’ll talk specifically about those tests.

Just something that’s on the horizon, is just coming out now, and probably very soon it will be more available — there is actually the ability now to draw mother’s blood and look inside of her blood and see some fetal DNA cause the placenta sheds little bits of DNA into mom. And so it takes a lot of blood, but you can draw mom’s blood and then look at baby. So it’s kind of a neat thing and that’s probably what we’ll end up doing more than an amniocentesis before long.