When you find out you’re pregnant, one of the best things you can do is start prenatal care -- a series of routine visits with your doctor or a certified nurse midwife to check on the health of you and your baby. You can ask questions about what to expect, and you’ll get advice on how to best care for yourself. Your doctor will also look for any problems, so you can catch and treat them as early as possible.
During the first trimester of pregnancy, there are two types of tests you can get to check for any problems with the fetus:
- Screening tests tell you how likely it is that your baby has Down syndrome. For example, you may find out that there’s a 1 in 100 chance that your baby has it.
- Diagnostic tests tell if your baby actually has it -- it’s a clear yes or no.
There are pros and cons to both types of tests. Screening tests don’t give you a definite answer, but diagnostic tests have a small risk of causing a miscarriage. Typically, you might start with a screening test. Then, if it looks like Down syndrome is a possibility, you might get a diagnostic test. These tests should be conducted alongside prenatal counseling to understand their results.
It’s your choice which tests to get, and you don’t have to get any of them. Some parents want to find out because they feel it will help them get ready. Others don’t feel they need to know. If you’re not sure what to do, your doctor or a genetic counselor can help.
Screening Tests
There are a few types of screening tests you can get.
First trimester combined test. You typically get this one sometime between the 11th and 14th week of pregnancy. It has two parts:
- A blood test looks for what doctors call “markers,” meaning proteins, hormones, or other substances that could be a sign of Down syndrome.
- Ultrasound looks at the fluid in an area of the baby’s neck called the “nuchal fold.” If the fluid level is higher than normal, it could be a sign of Down syndrome.
Integrated screening test. For this one, you get two tests taken at different times. The first one is just like the first trimester combined test. Then, during weeks 15-22, you get another blood test called the “quad screen.” It looks for four different markers that could be signs of Down syndrome.
If you want to be a little more certain of the results, you’d get this test instead of just the first trimester combined test.
Cell free DNA. DNA is what your genes are made of, and some DNA from the fetus ends up in the mother’s blood. This test looks at that DNA for signs of Down syndrome. You can get this test starting at 10 weeks, but it’s mainly used for women who are more likely to have a baby with Down syndrome.
Diagnostic Tests
These types of tests look at the baby’s chromosomes to check for Down syndrome. A “positive” result means your baby most likely has Down syndrome. A “negative” means your baby most likely doesn’t have it. Diagnostic tests have some risk of causing a miscarriage.
Amniocentesis (“amnio”) tests a sample of amniotic fluid, which surrounds your baby in the womb. Your doctor gets the sample by placing a needle through your belly.
There is a slight risk of miscarriage -- about 0.6% -- with a second-trimester amnio, while research shows the risk being higher before 15 weeks of pregnancy.
Chorionic villus sampling (CVS) tests cells from the placenta, which passes nutrients from mother to baby. Your doctor gets the cells either through your cervix or with a needle through your belly. It can be done at 10 to 12 weeks -- earlier than you can get an amnio -- but has a slightly higher chance of causing a miscarriage or other problems.
Cordocentesis, also called “percutaneous umbilical blood sampling,” or PUBS, is done at 18 to 22 weeks. Your doctor uses a needle to take blood from the umbilical cord. This procedure has about a 1.4% to 1.9% chance of miscarriage , more than the other tests, so it’s only done if the others don’t give clear results.
Genetic Counseling
If you need help understanding the results, you might want to talk to a genetic counselor. They’re highly trained in genetic conditions, as well as helping people talk through challenging issues.
They can speak to you about risks, walk through possible results, and help you figure out which tests might make the most sense for you. If you have a higher risk of having a baby with Down syndrome, you might want to talk to a genetic counselor before you get pregnant, but it can be very helpful after, too.