Multiple Marker Screening - A Prenatal Blood Test
NOTE: Below are some facts about MULTIPLE MARKER Screening, a test offered to pregnant women. If you have any questions after reading this, please ask your HEALTH CARE PROVIDER. Remember, it is your decision whether to have this test or not.
What is the Multiple Marker Screening Test and why is it done?
This blood test helps identify pregnant women who are at increased risk for having a baby with either a neural tube defect, Down syndrome or Trisomy 18. It is a blood test that is usually done at 15 through 21 weeks of pregnancy. Four different substances produced by the fetus (growing baby), called alpha-fetoprotein (AFP), unconjugated estriol (uE3), human chorionic gonadotropin (hCG), and Inhibin A (Inh-A) are measured in the mother's blood. A positive (abnormal) test result does not necessarily mean that your baby has a problem. However, additional testing may be suggested.
What are neural tube defects?
Neural tube defects (NTDs) are defects of the spinal cord and/or the brain. The two common types of NTDs are "anencephaly" and "spina bifida." Anencephaly occurs when the baby's brain and skull do not develop normally. These babies are usually stillborn or die shortly after birth. Spina bifida is a birth defect occurring when the spine does not close completely. NTDs occur in about 1-2 of every 1,000 births. The Multiple Marker Screening test can detect about 75% of NTDs.
What is Down Syndrome?
Down syndrome is a birth defect that causes mental retardation. It is caused by having an extra #21 chromosome and occurs in about one of every 800 births. The Multiple Marker Screening Test can detect about 75% of these pregnancies in women under the age of 35 and 85-90% of these pregnancies in women age 35 or older.
What is Trisomy 18?
Trisomy 18 is a birth defect that causes mental retardation along with other serious medical conditions. It is caused by having an extra #18 chromosome and occurs in about one of every 3,000 births. The survival rate for this condition is very low. The Multiple Marker Screening Test can detect 60-80% of Trisomy 18 fetuses.
How is the Multiple Marker Screening Test Done?
The test requires taking a sample of blood from the mother, usually at 15-21 weeks of pregnancy. The laboratory tests the blood sample to see how much AFP, uE3, hCG and Inh-A are present. The level of AFP is used to determine the risk of the fetus having a neural tube defect. The levels of AFP, uE3, hCG, and Inh-A, plus the mother's age, are all used to determine the risk of the fetus having Down syndrome. The levels of AFP, hCG and uE3 plus the mother’s age, are all used to determine the risk of the fetus having Trisomy-18.
What if my test is positive?
Your health care provider will discuss the results with you. Further tests will likely be suggested. In most cases, an ultrasound study (sonogram) will be recommended if you have not already had one. Sonograms can sometimes explain a positive test by finding that your pregnancy is either further along or not as far along as expected. Carrying twins may also explain a high AFP level.
If the sonogram does not explain your test result, a repeat sample, genetic counseling, amniocentesis and/or a more detailed ultrasound may be suggested. Amniocentesis is a test where a small sample of the amniotic fluid that surrounds the fetus is obtained. This sample can be tested to diagnose Down syndrome, Trisomy 18 and neural tube defects.
If these diagnostic tests are recommended, you will be able to discuss them with a physician or genetic counselor who will explain them completely and answer your questions. You will be able to choose whether or not you want further testing.
Remember, fewer than 5 out of every 100 women with a positive test result are carrying a fetus with a neural tube defect, Down syndrome or Trisomy18.
If the Multiple Marker Screening Test is negative, does that mean everything will be all right with the baby?
A negative (or normal) result can be reassuring and gives your health care provider useful information, but it does not guarantee a normal baby. The Multiple Marker Screening Test will detect about 75% of fetuses with neural tube defects, about 78-80%, overall, of fetuses with Down syndrome and about 60-80% of fetuses with Trisomy 18. Remember, some fetuses with neural tube defects, Down syndrome or Trisomy 18 will not be detected by the enhanced Multiple Marker Screening test. Also, many other birth defects cannot be diagnosed by this test.
Enhanced Multiple Marker Screening is another way we can help provide optimal care for you.
The test is simple and safe -- just a blood test.
It gives your health care provider valuable information about your pregnancy and your developing baby, and may alert them to the presence of twins, a change in your delivery date, or other conditions which may alter your prenatal care.