Maternal Serum Screening/Alpha-fetoprotein Test
Along with numerous other tests you will be offered as part of your prenatal care, your health care provider will likely ask you if you would like a maternal serum screening test or an alpha-fetoprotein (AFP) test. Like chorionic villous sampling and amniocentesis, maternal serum screening and AFP can offer you valuable information about your developing baby. However, it is up to you whether or not you want to have these tests done.
A protein produced by your baby’s liver, alpha-fetoprotein can be found in your blood. This simple blood test is used as a screening tool to check for neural tube defects, including spina bifida and ancephaly. However, this test can also alert you and your health care provider to the possibility of your baby having Down Syndrome or Turner Syndrome, placental problems, and kidney or urinary tract abnormalities among other issues. This test is optional and is very safe to perform without increased risk to you or your baby. It can be done between the 15th and 17th week of pregnancy.
What is Maternal Serum Screening?
Maternal serum screening is an optional blood test done on pregnant women to check for certain neural tube defects, such as spina bifida, or birth defects, like Down syndrome. Maternal serum screening is also known as a multiple marker screening test or triple screen because it measures levels of several substances in the blood. The test is usually conducted between 15 and 18 weeks into pregnancy.
What does the Test Assess?
In addition to measuring your levels of AFP, maternal serum screening also measures the hormones estriol and human chorionic gonadotropin (hCG), which are also produced by your baby and enter into your bloodstream. When AFP, estriol and hCG are measured together, the test is known as a triple screen. Because more hormones are measured, maternal serum screening is thought to be more accurate than measuring just the alpha-fetoprotein level. For this reason, it is used more often than the AFP test.
A quad screen is identical to the triple screen except that this test also measures the levels of inhibin-A in your system The quadruple test is used to give a more accurate assessment of your baby’s risk of having Down Syndrome. The test has about an 80% accuracy rate in indicating a baby’s risk of Down Syndrome. Amniocentesis can be used to confirm the diagnosis.
What the Results Mean
If you have received an abnormal test result, don’t panic. Abnormal test results indicate that your baby has an increased risk of neural tube defects or birth defects and that additional diagnostic testing is required. It does not mean that your baby will definitely be born with a birth defect or anomaly. In fact, only 1% to 2% of women who have an abnormal test result will go on to have a baby with a birth defect.
If you are found to have higher levels of AFP protein, it may indicate the presence of neural tube defects or other birth defects in your baby. Lower AFP levels suggest that your child may have Down’s Syndrome or some other chromosomal abnormality. In some cases, abnormal test results may only appear because the baby is older or younger than originally determined. Another reason for an abnormal test result is the presence of multiple births, such as twins or triplets. Smoking and drinking alcohol can also cause high levels of AFP to appear in the blood.
Abnormal Test Results
Starting in the 14th week of pregnancy, the level of AFP begins to rise. That is why it is important to accurately gage the gestational age of the fetus. So just what are abnormal results? Well, the average amount of AFP in a pregnant woman of 15 to 22 weeks is 19 to 75 international units per millimeter. If you are found to have exceptionally high or low AFP values, further testing, such as an ultrasound, will be used to determine the cause.
Who is a Candidate for the Test?
Alpha-fetoprotein levels are partly determined by a woman’s age, race, weight and if she has diabetes. You are a prime candidate to have this test if you:
- Have a history of birth defects in the family
- Are 35 years or older
- Have used harmful medications during pregnancy
- Have diabetes
How is the Test Done?
Whether you decide to have an AFP test, triple screening or maternal serum quad screening done, the test will be performed the same way. A sample of blood is taken from your arm and is sent to a medical laboratory for assessment. Your results should be ready within one week.
Pros of Maternal Serum Screening
If you are considering having this test done, here are some of the advantageous:
- Can help you make decisions about your baby
- Can detect twins, triplets, and higher-order multiple births, allowing you to receive the appropriate care
- Can help you make special arrangements for the birth of your child if necessary
- Can help you choose between a caesarean or vaginal delivery
Cons of Maternal Serum Screening
Despite the benefits of the test, there are some disadvantageous that are important to consider.
- Tests have a high level of "false-positive" results
- May present complications in those with bleeding disorders
- May cause a bruise at the needle site
- Testing can be expensive depending on the results
- Can lead to amniocentesis or chronic villus sampling which increases your risk of miscarriage
Remember, maternal serum screening is an optional test. Discuss with your health care provider and partner all the pros and cons of testing and what the possible test results will mean to you before deciding whether to have the test.