If you know that you want a diagnostic test, then you can skip screening tests and decide whether to have chorionic villus sampling (CVS) or to choose amniocentesis.
Screening tests for birth defects include blood tests and a certain type of ultrasound. Depending on the type of screening you have, the test can help your doctor estimate the chance that your baby may have Down syndrome, neural tube defects, or certain rare genetic problems. The blood tests are used to look for the amount of certain substances in your blood. The doctor uses an ultrasound to look for certain changes in your baby.
Other things are considered along with the test results to estimate the chance of a problem. For example, your doctor will look at your age, weight, and race, and how far along your pregnancy is.
If one of these tests shows a higher-than-normal chance of a birth defect, you would then decide whether to have a diagnostic test—chorionic villus sampling (CVS) or amniocentesis. These tests can show for sure if there is a problem. Diagnostic tests involve taking some of the baby's cells to look at the genes and chromosomes. But diagnostic tests have a small risk of causing a miscarriage.
The American College of Obstetricians and Gynecologists recommends that all women be offered a screening test for Down syndrome. The risk of having a baby with a genetic condition increases as a woman gets older.
If you choose to have a test for birth defects, you may want to talk with a genetic counselor. He or she can talk with you about your test options and about the reasons to have or not have tests.
Screening tests may be done in the first or second trimester of pregnancy.
First trimester screening tests let you find out about Down syndrome early in your pregnancy—between 10 and 13 weeks. But they aren't used to look for neural tube defects. This screening combines the results of two tests:
A newer screening test—called cell free fetal DNA—looks at fetal DNA in a pregnant woman's blood. It can be used to look for Down syndrome and trisomy 18. It also may find trisomy 13, which causes intellectual disability and heart defects, among other problems. This test is an option for women who are at high risk for having a baby with certain genetic conditions. But it can't help find other birth defects, such as neural tube defects. It's not used as a general screening test. And it's not available everywhere.
Second-trimester screening—done between 15 and 20 weeks of pregnancy—can be used to look for Down syndrome and neural tube defects.
First-trimester screening (nuchal translucency combined with blood tests) correctly finds Down syndrome in 82 to 87 out of 100 fetuses that have it. This also means that these tests miss it in 13 to 18 out of 100 fetuses.1
An ultrasound can find neural tube defects up to 99 out of 100 times.2 It won't find these problems 1 time out of 100. But ultrasound isn't as good at finding Down syndrome or genetic diseases.
The triple or quad screen finds 80 out of 100 fetuses with neural tube defects, such as spina bifida, and about 90 out of 100 with anencephaly.2 The test misses 20 out of 100 fetuses with spina bifida and 10 out of 100 with anencephaly.
The quad test finds Down syndrome almost 81 out of 100 times. It doesn't find it 19 out of 100 times.3 The quad test is more likely to find Down syndrome and may be less likely to be false-positive than the triple screen.
The integrated screening test (first-trimester tests plus the quad screening in the second trimester) correctly finds Down syndrome in about 95 out of 100 fetuses who have it. This also means that the test misses Down syndrome in 5 out of 100 fetuses.1
Normal results tell you that there is no need for more tests unless you have another concern, such as a known genetic disease in your family.
Positive results tell you that there is a higher-than-average chance of a birth defect. You will be offered a diagnostic test, such as chorionic villus sampling (CVS) or amniocentesis, to find out for sure if there is a problem.
Or you may decide not to have any more tests.
If a birth defect is found, you decide where to go from there. You may choose to learn all you can about raising a child with Down syndrome or a birth defect. Or you may decide to end the pregnancy.
With the blood tests, there is little or no physical risk. A fetal ultrasound has no known risks.
Having tests may make you worry. There is a chance that the test could show that there's a problem when there isn't one. This is called a false-positive test result. Or the test could miss a problem. This is a false-negative test result.
A positive result (meaning there could be a problem) could lead you to have a diagnostic test, which has a small risk of causing a miscarriage.
But most women have normal test results. Even when the test result is positive, most pregnancies turn out to have no problems.
If you don't have a screening test to diagnose a birth defect, your baby could have a problem that you don't find out about until birth.
Your doctor might recommend a screening test if:
|Have a screening test||Don't have screening|
|What is usually involved?|
|What are the benefits?|
|What are the risks and side effects?|
Are you interested in what others decided to do? Many people have faced this decision. These personal stories may help you decide.
These stories are based on information gathered from health professionals and consumers. They may be helpful as you make important health decisions.
"I know that I'm at a higher risk of having a baby with Down syndrome because of my age. My husband and I don't have any risk factors for having a child with other birth defects. If the screening tests weren't available, I would probably have an amniocentesis even though it has some risks. But since I can have the screening tests, I've decided to start with that and then make a decision about amniocentesis based on the results."
— Rachel, age 37
"I'm not really worried about things like birth defects that might or might not happen. I don't have any risk factors for having a baby with a birth defect. And I know a lot of women who have had amniocentesis and other tests who spent a lot of time worrying, only to have healthy, normal babies. I feel like the best thing I can do is take good care of myself, stay alert for any signs that there is a problem, and enjoy my pregnancy."
— Yvonne, age 31
"My neighbor had her first baby at our rural community hospital. The baby had spina bifida, and they rushed her by ambulance to the nearest city and then by helicopter to a center that treats babies with this problem. My neighbor had to follow her later on and so was away from her baby at a really traumatic time. It was such a scary experience for her. I am definitely going to have the screening tests and find out my risk of having a baby that needs special care so we can plan ahead."
— Candace, age 26
"My husband and I want to have the most definitive information possible to make decisions about my pregnancy. So we are going to start with the chorionic villus sampling. I know it's a little more risky, but we feel like we need as much information as early as we can get it. It took us a little longer than we expected to become pregnant. If there is any chance that the fetus has a birth defect, we want to know that as soon as we can so we can make the best decision for us about whether to continue this pregnancy or end it and give ourselves a chance to try again."
— Elena, age 37
Your personal feelings are just as important as the medical facts. Think about what matters most to you in this decision, and show how you feel about the following statements.
Reasons to have a screening test
Reasons not to have the test
I want to know if there's a chance that there could be a problem.
Knowing that there's a problem wouldn't change my birth or parenting plans.
I'm not worried that the test could show a problem when there isn't one.
I'm worried that the test could show a problem when there isn't one.
I want to just have the blood test or ultrasound.
I'd rather have CVS or amniocentesis to find out for sure if there's a problem.
My other important reasons:
My other important reasons:
Now that you've thought about the facts and your feelings, you may have a general idea of where you stand on this decision. Show which way you are leaning right now.
Having a screening test
NOT having a screening test
1. A screening test can tell me for sure if there's a problem with my fetus.
2. These tests could show that there is a chance of a problem with my baby when there isn't one.
3. If a screening test shows no chance of a problem, I probably won't need to have more tests for birth defects.
1. Do you understand the options available to you?
2. Are you clear about which benefits and side effects matter most to you?
3. Do you have enough support and advice from others to make a choice?
1. How sure do you feel right now about your decision?
2. Check what you need to do before you make this decision.
3. Use the following space to list questions, concerns, and next steps.
|Primary Medical Reviewer||Sarah Marshall, MD - Family Medicine|
|Specialist Medical Reviewer||Siobhan M. Dolan, MD, MPH - Reproductive Genetics|