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 blood sample is drawn 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’s 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’ve undergone the multiple marker test and received abnormal results, there’s 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.
If your results show high levels of AFP, pointing to a possible risk of spina bifida or another neural tube defect, your 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 you’re carrying multiples. The doctor also may offer amniocentesis, which is the withdrawal of amniotic fluid from the uterus for further testing.
If your multiple marker screen results reveal low levels of AFP and estriol and high levels of hCG and inhibin-A, you have 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. That’s why pregnant women are offered amniocentesis so chromosome testing can be done on the fetal cells found in the amniotic fluid.
Remember, 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 doesn’t necessarily mean that there’s a birth defect, but that there’s a need for more evaluation.
If you have questions or concerns about multiple marker testing, talk to your doctor or seek the advice of a genetic counselor.
© 2012. Article adapted from The Nemours Foundation/KidsHealth®. Used under license.