Iowa Health Book: Obstetrics and Gynecology
Seeing your doctor early to begin prenatal care is an important part of preparing for the birth of your baby. There are tests designed to provide you and your doctor with information about your pregnancy and your developing fetus. Although most babies are born healthy, about 3 to 4% are born with a birth defect. Frequently this happens without warning, and families and doctors are not prepared for this difficult experience.
The MSAFP (maternal serum alpha-fetoprotein) screen is a test available to all women early in pregnancy. This test can identify a woman with an increased risk to have a fetus with certain kinds of birth defects or to develop a problem later in pregnancy.
This pamphlet is designed to help you understand the screening process. Read it with your partner and then discuss your questions with your doctor or nurse.
What is AFP?
Alpha-fetoprotein is a substance produced by every fetus as it grows. This substance is passed into the amniotic fluid that surrounds the fetus and from there into the mother's bloodstream. Nothing the mother does alters the level of this protein. It is not related to the protein in the mother's diet, but comes directly from the fetus.
What is the MSAFP screen?
The MSAFP screen is a single blood test drawn between the fifteenth and twentieth week of pregnancy to measure the amount of AFP and two other hormones in the mother's bloodstream. The other hormones, E3 (estriol), and hCG (human chorionic gonadatropin), are also made by the fetus and placenta. The levels of these three hormones may be altered when a fetus has certain birth defects such as an open neural tube defect, an abdominal wall defect, or a chromosome problem such as Down syndrome.
For most women, the results of this screen will be negative and no further tests are ordered. This is reassuring, but does not guarantee the fetus is normal. The MSAFP screen is the first test in a series of tests that may be done. It cannot directly diagnose birth defects, but can help you and your doctor decide when other tests such as ultrasound and amniocentesis may be of value.
What is ultrasound?
Ultrasound (sonogram) uses sound waves to create pictures of the fetus. Careful measurements determine the age of the fetus, whether there is more than one fetus, and in some cases may reveal a birth defect.
What is amniocentesis?
Amniocentesis involves using a thin needle to withdraw fluid from around the fetus for testing. The fetal cells and AFP in this fluid are studied to diagnose birth defects such as neural tube defects and chromosome problems such as Down syndrome.
What are neural tube defects?
In the first weeks of pregnancy when the fetus is less than one inch long, the brain and spinal cord begin to form a structure along the fetal back known as the neural tube. The top of this tube develops into the head and brain, the rest becomes the spinal cord.
The two major types of neural tube defects are spina bifida and anencephaly. About one in 1,000 pregnancies in Iowa results in the birth of an infant with a neural tube defect. Half of these have spina bifida and half have anencephaly.
The effects from spina bifida (open spine) may range from mild to severe. The severity of the problem depends upon where the defect in the spinal cord is located. The problems may range from weakness of the leg muscles to actual paralysis. A higher defect on the spine will result in more paralysis in the legs. Because the nerves that direct bowel and bladder functions are at the base of the spinal cord, there may be problems with bowel and bladder control. Over 80 percent of newborns with spina bifida have hydrocephalus (water on the brain). Corrective surgery and physical therapy can help lessen the disability in these children so that some may lead relatively normal lives. In severe cases the baby is stillborn or dies soon after birth.
Anencephaly (open brain) occurs when the head and brain do not develop normally. Babies born with this condition are almost always stillborn or die soon after birth.
If the defect is in the spinal cord itself, but is covered by skin, the AFP will not leak into the amniotic fluid. These defects will not be detected by the blood test and the effects tend to be less severe.
What is Down syndrome?
Down syndrome is a birth defect caused by an extra number 21 chromosome in every cell of the body. Individuals with Down syndrome are mentally retarded and may have other physical problems such as heart defects. Any woman can have a fetus with Down syndrome, but it is known that Down syndrome and other chromosome problems happen more often as women get older.
What causes the MSAFP screen to be positive?
A screen is called positive if the hormone levels are too high or too low compared to the normal levels for that week of pregnancy.
What are the reasons for a positive MSAFP screen?
What if the MSAFP screen is positive low?
An ultrasound is done. If the ultrasound changes your due date the result of the screen may now be normal. The blood test is only repeated if the initial sample was drawn before fifteen weeks.
After ultrasound, about four percent of women will have a screen that remains positive low. They will be offered amniocentesis due to an increased risk for a chromosome problem in the fetus. The factors used to figure the risk for chromosome problems include maternal age and weight, fetal age (week of pregnancy), and the levels of AFP, E3 and hCG in the maternal blood.
What if the MSAFP screen is positive high?
An ultrasound is done. The blood test is repeated if the result remains elevated after ultrasound confirms or corrects the fetal age. About 70% of the repeated tests will be normal and no further testing will be needed.
What if the second test remains positive high?
About one to two percent of women will have a screen that remains positive high and will go on to have an amniocentesis. About one in thirty of these women will have a fetus with a potentially serious birth defect. Most often this will be a neural tube defect.
If the amniocentesis results are positive (abnormal) another ultrasound will be done to identify the extent and location of the defect. This information will be needed to provide you with accurate counseling about the problems the fetus may have.
If the amniotic fluid level is normal, but the MSAFP screen remains elevated, you may have an increased risk for problems later in the pregnancy. These problems are related to the function of the placenta and include early labor, a smaller than average baby and some other pregnancy problems. Most women with high AFP levels will still have healthy babies, but you should discuss your care with your doctor so you will know what to do if a problem occurs.
What can be done if a birth defect is discovered?
It is a shock to learn that your fetus has a birth defect. You will need information about the specific condition and any treatment that is available. There is no current treatment for neural tube defects or chromosome problems before the baby is born. There are two options to consider: You may begin to plan for the birth of a baby who may need intensive care at birth of you may elect to end the pregnancy.
What are the risks involved in the screening process?
Anxiety: Waiting for the results of a repeated test is a very anxious time for women who have had the MSAFP screen. It is natural to be afraid when considering the possibility of a problem with your baby. The results of all repeated blood tests are telephoned to the doctor's office the day they are completed. Fortunately, most women with a positive MSAFP screen will have healthy babies.
Pregnancy Loss: If the screening process leads to amniocentesis there is a small but real risk of pregnancy loss associated with this procedure. Ask the doctor who does your amniocentesis to discuss that possibility with you.
Summary
The MSAFP screen will provide information about your baby before it is born. It is a test available to all women between fifteen and twenty weeks of pregnancy. A negative screen provides reassurance that the risk for certain birth defects and pregnancy problems has been reduced. Even though most babies will be healthy, the period of testing is a stressful time. If a problem is detected you will need support and guidance. Discuss this with your doctor or nurse if you have questions. In addition you may call (319) 356-8892. An AFP nurse will return your call.
Written by Stanley Grant, R.N.
Revised April 1990