Occasionally either an abnormal ultrasound finding or an abnormal lab test result, such as non-invasive prenatal testing, will suggest that the baby’s at increased risk for a genetic condition.
There’s two ways that we can determine if the baby, in fact, has this abnormal genetic condition.
Unfortunately both are invasive and that can be quite scary to a family as they’re deciding whether or not to pursue these tests.
Chorionic Villus Sampling
Early in the pregnancy we can perform chorionic villus sampling. This is essentially a biopsy of the placenta.
This test is performed under ultrasound guidance so we’re watching the baby and the placenta, as well as the needle, the entire time. We do not actually go into the sack where the baby is, and we stay only in the placenta.
Remember that the baby and the placenta come from the same sperm and egg, so they should be genetically identical, which allows us to sample the placenta and not directly from the baby or the amniotic fluid.
The test is performed after 10 weeks of pregnancy and we can do it up through the 13th week of pregnancy. This gives us an opportunity to give early information.
Obviously invasive procedures do have some risk. The risk for this test is lower than most would expect.
If we perform three to 500 of these tests, roughly one woman would suffer a miscarriage directly related to the procedure itself.
Amniocentesis is a more commonly performed test, and many people have heard of this. Other ways we refer to it is an “amnio.”
Amnio’s are done later in the pregnancy after 15 or 16 weeks of gestation. The reason for this is because we’re taking a sample of the amniotic fluid. The pregnancy has to progress to a certain point in order for us to be able to get into the sac that’s around the baby.
We take a small sample of fluid, about a tablespoon, and send it off to the lab.
This test is also performed while ultrasound is watching continuously where the needle is and where the baby is.
We do not touch the baby during the procedure, and the baby will actually replace the fluid by peeing so they don’t miss it and they don’t even usually know we’re there.
The complications from amniocentesis are similar to that of early testing. About one out of every three to 500 procedures can cause a pregnancy loss.
Because of all of these risks we try to limit the number of patients who we recommend this test for, only to those that we think are at the highest risk of having a genetic condition, and where that information will help us in making decisions about how best to manage the pregnancy.