St. Luke’s Maternal Fetal Medicine

The Maternal Serum Multiple Marker Screen

This information is provided by St. Luke’s to answer some of the most common questions asked about a prenatal blood test know as the “maternal serum multiple marker screen.” If you have further questions, please talk to your health care provider.

Why am I being offered this test?
Most babies are born healthy, but sometimes babies are born with birth defects. This can happen even when the mother has taken good care of herself and when no one else in the family has had a birth defect. There are many special tests which can be done to find out if a baby has birth defects before it is born. Because most babies are normal it does not make sense to offer these special tests (which may have risks for pregnancy and which may be expensive) to all pregnant women. The maternal serum multiple marker screen blood test is used to give you and your health care provider the information you need to decide if more specialized testing is needed in your pregnancy.

What birth defects is the test looking for?
This test does not tell a woman if the baby will actually have a birth defect. It only tells the woman if her risks are greater than a certain cutoff. The test will be looking for signs that a baby might be at increased risk to have one of these abnormalities:

• Down syndrome. Down syndrome affects about 1 in 800 babies. It generally does not run in families. Babies with Down syndrome can have heart defects and other physical birth defects. People with Down syndrome have some degree of mental retardation.
  
• Spina bifida. Babies with spina bifida have a hole in the spine that may cause paralysis; the amount of paralysis varies from person to person. It affects 1 in 1000 babies. It generally does not run in families, but if someone else in your family has had spina bifida, you should tell your health care provider.
  
• Anencephaly. In anencephaly the skull and brain do not form completely. Usually babies with anencephaly die soon after birth. It generally does not run in families, but if someone else in your family has had anencephaly, you should tell your health care provider.
  
• Abdominal wall defects. In these conditions, there is a small hole in the baby’s stomach so that intestines can grow outside of the baby. Often these conditions can be corrected with surgery after birth. These conditions do not run in the family and may be more common in young women.
  
• Trisomy 18. Babies with trisomy 18 can have multiple birth defects and often die before they are a year old. Children who survive have mental retardation. Trisomy 18 does not run in the family.

This test does not look for all birth defects, and no test can guarantee that the baby will not have any birth defects.

How is the test done?
The test is done on a blood sample taken from a pregnant woman’s arm. The blood is drawn between 15 and 20 weeks after the first day of the woman’s last period. Results of the blood test are usually available one to two weeks after the test is drawn. Talk to your health care provider about when and how the results will be given to you.

How much does the test cost?
The cost will vary, but it usually costs about $200. Most insurance plans will cover this test, but you may wish to check with your insurance carrier.

What happens if I have a positive test?
If you have a positive result, you will probably be quite nervous. It is important to remember that most of the women who test positive actually have healthy babies. The information from the test will help you and your health care provider decide whether to have more tests done. Your care provider may also refer you to a genetic counselor to discuss the results and testing options in more detail. If you have a positive result you will probably be offered an ultrasound and you may be offered an amniocentesis. Most of the time the results of these tests come back normal.

How could I have a positive blood test if the baby is normal?
There are many reasons why a healthy baby could have a positive test. If your due date is sooner or later than you think it is, the result may not be accurate. Sometimes a result will be positive if the woman is carrying twins and doesn’t know it. A normal baby can sometimes have a positive result just because of day to day changes in normal pregnancy. Many women have friends or relatives who have had a positive test when the baby was fine. This can happen. It is important to remember that this test does not tell if there is actually a problem in the baby; it only tells if more testing should be offered to a woman.

What happens if I have a negative test?
If the test is negative, then you are probably not at high risk to have a baby with one of the birth defects the test looks for. But the blood test is not perfect, and there is still a small chance that the baby could have one of these problems.

Do I have to have this test?
No, you can decide if you want to have this test done. The testing is your choice. You should discuss your decision with your health care provider.

If I am 35 or older, should I have this test done?
Because women 35 years of age and older have a higher than average risk to have a baby with a chromosome abnormality (such as Down syndrome), these women should be offered amniocentesis. Amniocentesis is the most accurate way to test for chromosome abnormalities. For women 35 and above who are thinking about having amniocentesis but are concerned about its 1/200 miscarriage risk, sometimes the information from the blood test can help them decide if amniocentesis is right for them. But there are some disadvantages of using the blood test in women who are 35 years of age or older. First, waiting for blood test results may mean that the amniocentesis is done later and that results may not be available as early in the pregnancy as a woman may want. Second, because of how the blood test is set up, women over 35 have a higher chance of having a positive blood test than younger women; this may create added anxiety for these women. A 20-year-old woman has a 2% chance of having a positive blood test; a 35-year-old woman has a 13% chance of having a positive blood test and a 40-year-old woman has a 36% chance of having a positive blood test result. Third, the blood test does not test for as many conditions as the amniocentesis and the amniocentesis is more accurate. Therefore, occasionally there will be a normal blood test, but the child is born with a condition that could have been found by amniocentesis.

What if I still have questions?
If you have more questions about this test, please discuss them with your health care provider. You may also contact us at:

St. Luke’s Maternal Fetal Medicine
333 North First Street, Suite 150
Boise, ID 83702
(208) 381-3088