A screening test can lead to an early diagnosis and treatment. There are a number of tests to look for abnormal factors in chromosomes (DNA). There are no cures but it may help you make future health choices. It can also help you get ready for the care your baby will need.

Talk to your doctor or midwife about these tests. Learn the benefits and harms of testing before you decide. These are the tests:

Maternal Blood Screening

The mother's blood will be sampled at 15-18 weeks of pregnancy. It is tested for the levels of certain substances in your blood. These substances can hint at a chromosomal issue in the baby. It does not mean that there is a problem. It only suggests a higher than normal risk of one.

If the levels are abnormal, you may be offered other tests. These tests can give you more detail and a better diagnosis. The next steps may be an ultrasound and amniocentesis.

AFP (Alpha-Feto Protein) Screen

The AFP screen is the most common test for birth defects. The fetus’ liver and yolk sac make AFP. It can enter the mother’s bloodstream during pregnancy. This blood test is done at 16-18 weeks of pregnancy. It is a safe test. You should have the results within one week.

Higher than normal AFP levels are linked to a specific type of birth defect. This is called a neural tube defect. It is a problem with how bones form around the spinal cord. AFP leaks out of the damaged spinal column and into the mother's blood. This causes higher levels of AFP than normal. A neural tube defect can lead to spina bifida and problems with brain growth.

A lower than normal AFP level can suggest Down syndrome or another chromosome related issue.

This screening test is common but it is not exact. There is a high rate of false results. This means where that the test does not show a problem when one may exist. If the levels are abnormal, you may be given other tests. These tests can give you more detail and a better diagnosis. The next steps may be an ultrasound and amniocentesis.

Triple Screen

The triple screen tests the mother's blood between 15-17 weeks of pregnancy. It is done to look for three specific substances:

  • Alpha-fetoprotein (AFP)
  • Human chorionic gonadotropin (hCG)—hormone made within the placenta
  • Estriol—an estrogen made by both the fetus and the placenta

These substances are all normally found in certain amounts. If the levels are too high or too low, it may suggest a problem.

This test may be recommended for women who:

  • Have a family history of birth defects
  • Are 35 years of age or older
  • Used harmful medicines or drugs during pregnancy
  • Have diabetes and use insulin
  • Had a viral infection during pregnancy
  • Have been exposed to high levels of radiation

The doctor will look at the results of this test as well as the mother's age and ethnicity. This will help to find out the risk of a genetic disorder. The triple test can sometimes also find other problems like:

  • Heart and digestive system defects
  • Whether the mother is carrying twins
  • Risks of premature birth, pre-eclampsia, and miscarriage

Quad Screen

The quad screen looks for four specific substances in the mother's blood:

  • Alpha-fetoprotein (AFP)
  • Human chorionic gonadotropin (hCG)—hormone made within the placenta
  • Estriol—an estrogen made by both the fetus and the placenta
  • Inhibin-A—a protein made by the placenta and ovaries

This test is like the triple screen. But the quad test may be more exact for Down syndrome. The quad tests also have a lower rate of missing problems.

Ultrasound

Ultrasound is used to make pictures of the fetus. It is often done 10-14 weeks into your pregnancy. The doctor will look for the neck fold of the baby. The fold is larger than normal in a baby with Down syndrome or Turner syndrome.

Amniocentesis

This test removes a small amount of fluid that surrounds the baby. It is done at 15-18 weeks of pregnancy.

Your doctor will put a thin needle into your belly. An ultrasound will help to guide the needle to the right spot. A small amount of the fluid is drawn out. There is a small risk of miscarriage.

This test is advised for women who:

  • Are over 35 years of age
  • Have a prior child with a birth defect that can be diagnosed by amniocentesis
  • Have a family history of a genetic disorder
  • Have an abnormal triple screen test result

Substances in the fluid may suggest certain genetic defects. It takes one to two weeks to get the results on chromosomal abnormalities. Other results are usually ready the next day.

Chorionic Villus Sampling (CVS)

CVS gives you more genetic detail than amniocentesis. It can be done earlier in pregnancy and gives quicker results.

CVS is a more invasive procedure. It is done between the 10th and 12th week of pregnancy. The doctor removes a tiny sample from the inside of the uterus. The sample comes from small areas that surround the fetus in the early weeks. This area later forms the placenta. The sample may be taken by putting a thin tube through the vagina and cervix. It may also be done by putting a needle through the abdomen.

There is a small risk of miscarriage. While the risk is fairly low, it is higher than the risk for amniocentesis. Vaginal bleeding is also common.

This test is advised for women who:

  • Are over 35 years of age
  • Have a child with a genetic defect
  • Have a family history of a genetic disorder
  • Have an abnormal first trimester screening

Revision Information

  • Reviewer: EBSCO Medical Review Board Kathleen A. Barry, MD
  • Review Date: 06/2018 -
  • Update Date: 07/31/2018 -