Alpha Fetoprotein Tests Protein and Hormones in the Mother’s Blood
If you decide to have the AFP test, a vial of blood will be drawn at your prenatal visit sometime between 15 and 17 weeks of pregnancy. The lab will then test your blood for the presence of alpha-fetoprotein which is produced in your baby’s liver. Your blood will also be tested for the levels of hormones secreted by the placenta, known as estriol and hCG.
Since three markers are tested in the mother’s blood, this is why the AFP is often referred to as the “triple screen” test. In some cases a fourth marker, the hormone inhibin A is also tested so the blood test then becomes a “quad screen.”
AFP Test Results – What do They Mean?
When the lab test results come back, your care provider will evaluate whether or not the levels of AFP and placenta hormones are what should be expected at that week of pregnancy for your age. So if the amount of AFP is higher or lower than expected, it can signal to the care provider that the mother is at a higher than expected risk of having a baby with a genetic problems.
It is important for expectant parents to know that a higher or lower than expected result on the triple screen does not indicate with certainty that a baby does or does not have a genetic defect or other problem. The AFP is simply a screening tool that requires further testing in order to confirm results.
AFP Test Results are Lower than Expected
If your AFP results come back lower than expected, it could indicate any of the following:
- You have a higher than expected risk for having a baby with Down’s Syndrome or other genetic defect
- You have a higher chance of having a miscarriage
AFP Test Results are Higher than Expected
If the results of your AFP or triple screen come back higher than expected, it can indicate that:
- You have a higher risk of having a baby with a neural tube defect such as spina bifida or anencephaly
- You are carrying twins
- Your due date in inaccurate
- You have a higher risk of preterm birth
AFP Triple Screen Accuracy
Like any tests done today, there is always a margin of error with prenatal testing. The AFP has a rate of false positives (meaning that the results show a higher risk when there is no defect) about 5-8% of the time. But the triple screen can also work the opposite way where there is a defect in the baby and the test does not identify it. This is known as a false negative and in the case of the AFP test, it happens about 35-40% of the time.
Because of these inaccuracies, your care provider may recommend following up the triple screen with an ultrasound that measures the thickness of the fold in the back of the baby’s neck, known as the nuchal fold translucency. In some cases, an amniocentesis may also be offered to confirm results from the AFP.
Alpha-Fetoprotein Test is Optional, Not Mandatory
Just because prenatal tests like the Alpha-fetoprotein are offered or even recommended by your care provider, it does not mean you are required to have it done. All prenatal testing, whether they are screening or diagnostic tools, is a personal choice. Parents ought to know that there are both good reasons to have the AFP test as well as good reasons to decline it.
Disclaimer: The information contained in this article is for educational purposes only and should not be used for diagnosis or to guide treatment without the opinion of a health professional. Any reader who is planning to make decisions about prenatal testing should contact a doctor for advice.