About the Multiple Marker Test
Between the 15th and 20th weeks of pregnancy, expectant mothers usually are offered a blood test called the multiple marker test. Sometimes called a triple screen or a quad screen, depending on the number of things measured, it also might be done in combination with blood tests and an ultrasound in the first trimester.
For the multiple marker screening, a sample of blood is drawn from the mother to measure the levels of:
- hCG (human chorionic gonadotropin), which is made by the placenta
- estriol, which is made by the placenta and the fetus
- alpha-fetoprotein (AFP), which is made by the fetus
Sometimes the level of inhibin-A, which is made by the placenta, also is measured. The levels of these substances can help doctors identify a fetus at risk for certain birth defects, including neural tube defects (like spina bifida) and some chromosomal abnormalities (like Down syndrome).
In determining the results of the test, doctors take into account factors such as:
- the mother's age, weight, and ethnicity
- whether she has diabetes
- if she is having twins or other multiples
- the gestational age of the fetus
These variables can affect the levels of the substances being measured and the interpretation of the test results, so the accuracy of this information is vital. If any of the information is incorrect, the screening results might be inaccurate.
Receiving Abnormal Results
If you have undergone the multiple marker test and received abnormal results, there is no need to worry yet. Just because the test is abnormal doesn't mean that your child has a birth defect. Rather, an abnormal screen indicates that the fetus should be evaluated further.
Usually, when a pregnant woman's results show high levels of AFP, pointing to a possible risk of spina bifida or another neural tube defect, her doctor will order a detailed ultrasound to examine the fetus, including the fetal skull and spine. In addition, an ultrasound can confirm the age of the fetus and whether the woman is carrying multiples. The doctor also may offer amniocentesis, which is the withdrawal of amniotic fluid from the uterus for further testing.
If a woman's multiple marker screen results reveal low levels of AFP and estriol and high levels of hCG and inhibin-A, she has an increased risk of having a baby with Down syndrome. The next step is often an ultrasound to confirm the baby's due date and to look for any obvious abnormalities. Unfortunately, ultrasound is not a very good test for detecting Down syndrome. For this reason, pregnant women are offered amniocentesis so chromosome testing can be done on the fetal cells found in the amniotic fluid.
In general, remember that the multiple marker test is just a screen. It can identify many fetuses that are at risk for certain birth defects, but will not identify them all. A positive screen does not necessarily mean that there is a birth defect, but that there is a need for more evaluation.
If you have any questions or concerns about multiple marker testing, talk to your doctor or seek the advice of a genetic counselor.
Reviewed by: Larissa Hirsch, MD
Date reviewed: May 2010
|National Society of Genetic Counselors This organization represents the genetic counseling profession through research, advocacy, and education.|
|March of Dimes The March of Dimes seeks to prevent birth defects, infant mortality, low birthweight, and lack of prenatal care.|
|American College of Obstetricians and Gynecologists (ACOG) This site offers information on numerous health issues. The women's health section includes readings on pregnancy, labor, delivery, postpartum care, breast health, menopause, contraception, and more.|
|Lab Tests Online This non-commercial site was developed by laboratory professionals to educate caregivers, patients, and patients' families about lab tests.|
|Birth Defects Many parents assume that all birth defects are severe or even fatal, but many are treatable, often immediately after birth - and sometimes even before the baby is born.|
|A Guide for First-Time Parents If you're a first-time parent, put your fears aside and get the basics in this guide about burping, bathing, bonding, and other baby-care concerns.|
|Down Syndrome Down syndrome is a condition in which extra genetic material causes delays in the way a child develops, both physically and mentally.|
|Prenatal Tests Every parent-to-be hopes for a healthy baby. A wide array of tests for pregnant women can help to reassure them and keep them informed throughout their pregnancies.|
|A Week-by-Week Pregnancy Calendar Pregnancy is an exciting time. Our week-by-week illustrated pregnancy calendar is a detailed guide to all the changes taking place in your baby - and in you!|
|Spina Bifida Spina bifida is a birth defect that involves the incomplete development of the spinal cord or its coverings. It's usually detected before a baby is born and treated right away.|
Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
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