Prenatal testing in pregnancy

When you are pregnant, prenatal tests give you information about your health and the health of your baby. They help detect any problem that may affect them, such as birth defects or genetic diseases. The results can help you make the best health care decisions before and after your baby is born.

Prenatal tests are helpful, but it's important to know how to interpret their results. A positive test result does not always mean that your baby will be born with the disease. You'll want to talk to your doctor, midwife, or other health care provider about what the tests mean and what you should do when you get the results.

Doctors recommend certain prenatal tests for all pregnant women. Only a few women will need additional screening tests to detect certain genetic problems.

Routine prenatal tests

There are various prenatal tests that you can have during the first, second and third trimesters. Some check your health and some get information about your child.

Throughout your pregnancy, you will have routine checkups to make sure you are in good health. Your health care provider will test samples of your blood and urine for certain conditions, including:

HIV and other sexually transmitted diseases
Anemia
Diabetes
Hepatitis B
Preeclampsia, a type of high blood pressure

They will also check your blood type and the presence of a protein called the Rh factor in your blood cells.

Pap smear

Testing for group B strep. Your doctor will take a swab of the skin in and around your vagina to check for this type of bacteria. This usually happens in the last month before giving birth.
Ultrasound. This technology uses sound waves to take pictures of your baby and your organs. If your pregnancy is going well, you will do this twice: once at the beginning to see where you are and a second time around 18-20 weeks to check your baby's growth and make sure his organs are developing properly.

Prenatal genetic testing

Doctors may also use prenatal tests to look for signs that your baby is at risk for certain genetic disorders or birth defects. You don't have to take these tests, but your doctor may recommend some to make sure your child is healthy.

They are especially important for women who are at increased risk of having a baby with birth defects or genetic problems. This is you if you:

Are over age 35
Have had a premature baby or a baby with a birth defect before
Have a genetic disorder or one that runs in your family or the other parent’s family
Have a medical condition like diabetes, high blood pressure, a seizure disorder, or an autoimmune disorder such as lupus
Have had miscarriages or stillborn babies in the past
Have had gestational diabetes or preeclampsia when you were pregnant before

Some prenatal genetic tests are screening tests. They tell you if your baby is at increased risk for a certain disorder or disease, but they can't tell you for sure if they will be born with that disease. Other "diagnostic" tests will give you a more accurate answer. You usually get this type after a positive drug test result.

To start, your doctor may test you and the other parent of the child for genes that cause certain genetic diseases, such as cystic fibrosis, Tay-Sachs disease, sickle cell anemia, and others. If you both have the gene for one of these diseases in your DNA, you can pass it on to your child, even if you don't have the disease itself. The exam is called the carry test.

Your doctor may use one or more different screening tests to see if your child has a genetic problem, including:

Ultrasound. You will already have one early in your pregnancy to make sure everything is going well. But if you're having a high-risk pregnancy, you'll need this test more often. Around 11-14 weeks, doctors may use it to examine your baby's neck. Wrinkles or thick skin may mean a higher risk of Down syndrome. At the same time, the doctor may take a blood sample from you.
Integrated screening. This test has two phases. In the first part, doctors combine the results of your baby's neck ultrasound and the blood tests you had between 11 and 14 weeks. They will then take a second blood sample between 16 and 18 weeks. The results measure your child's risk of developing Down syndrome and spina bifida, a disease of the spinal cord and brain.
Sequential screen. This is similar to integrated screening, but your doctor reviews the results with you right after the first phase at 11-14 weeks. It's not as accurate as the longer test, but it lets you know about the risk to your child earlier. If the screening shows there may be a problem, your doctor will run other tests to find out for sure. If he finds no risk, you will likely have a second blood test at 16-18 weeks to be on the safe side.
Triple or quadruple screening test. Doctors check your blood for hormones and proteins from your baby or the placenta, the organ that brings them oxygen and nutrients. The test may look for three different substances or four. A certain number means your baby is at higher risk for a birth defect or genetic disease. This test is done in the second trimester, usually between 15 and 20 weeks.
Cell-free fetal DNA test. Doctors use this test to look for your baby's DNA in your blood and test it for Down syndrome and two other genetic conditions, trisomy 18 and trisomy 13. You can do this after 10 weeks of pregnancy. Doctors do not recommend it to all women, usually only high-risk pregnant women. It is not available everywhere and some health insurance policies do not cover it. Ask your doctor if you need this test.

Other tests

If you get a positive screening result, your doctor may use other tests to look for a problem.

Amniocentesis. Using a thin needle in your abdomen, your doctor will take a sample of the fluid surrounding your baby and check it for genetic disorders or birth defects. The procedure carries certain risks. About 1 in 300 to 500 women have a miscarriage due to an amniocentesis. Your doctor can tell you if this is important to you.
Chorionic villus sampling. Doctors remove a small piece of the placenta by inserting a needle into the abdomen or a small tube into the vagina. They test the sample for Down syndrome and other genetic diseases. Only some high-risk women will need this test, usually if screening reveals a risk of a birth defect. The procedure will tell you exactly if there is a problem, but it also carries the risk of miscarriage, just like an amniocentesis. Ask your doctor if you need to have a chorionic villus biopsy.

What should I do after receiving the results?

Prenatal test results can help you make important health care decisions. But it's important to remember that many of them tell you that it's possible, but not necessarily, that your baby will be born with the condition. No test is 100% reliable.

Talk to your doctor about your results and what they mean. A genetic counselor can also help you decide what to do after a positive result and what life will be like for your child if they have the disorder.

Questions for the doctor

If your doctor recommends a prenatal test, consider ordering:

Why do I need these tests?
What will the results tell me? What will they not show?
What happens if I don't get the test?
What will I do with the results?
How accurate are the tests?
What are the risks?
How long will it take to get the results?
What does it feel like?
How much do they cost?
Will my insurance cover them?
Will anyone else (like my insurance company) have access to the results, especially of genetic tests?
What will the results mean for my family?
Can I decide not to get the results even if the test has already been done?
Where do I get the tests done?