The AFP QUAD + Test

What is the AFP+ Quad Test?

It is a maternal serum test done between the 15th and 22nd week of pregnancy that allows us to measure certain substances that come from the developing fetus and placenta and are present in the mother's serum. The substances that we measure are called alpha-fetoprotein (AFP), hCG, estriol, and inhibin-A. By finding out what the levels of these substances are in your serum, we can learn certain things about your developing baby.
 

What can the AFP+ Quad Test tell me about my pregnancy?

It can tell you whether you are at high risk for having a baby with either a neural tube defect, Down syndrome or Trisomy 18. Ultimately, about one in twelve patients will have a “screen positive” AFP+Quad Test result. If your test result is “screen positive” it does not necessarily mean that your baby has one of these disorders, but it does mean that your doctor will suggest some additional testing.

What are neural tube defects?

Neural tube defects are a group of birth defects which include open spina bifida and anencephaly. One or two babies out of every 1000 is born with a neural tube defect.

Open spina bifida is an incomplete closure of the spine. It varies in severity depending on where it's located on the spine and how big the opening is. Surgery to close the opening is usually performed shortly after birth and additional surgery is often necessary later in infancy and childhood. Open spina bifida usually causes some amount of paralysis from the waist down and interferes with bowel and bladder control. It often leads to a condition called hydrocephalus (water on the brain) and can sometimes cause mental retardation. Almost one third of babies born with open spina bifida will not survive past age five.

The level of AFP in the mother's serum tends to be elevated when there is a pregnancy affected by an open neural tube defect. About 90% of all pregnancies with open neural tube defects will be identified through AFP+ Quad Testing. Closed neural tube defects will not be picked up by AFP testing.

What is Down syndrome?

Down syndrome is a common birth defect occurring in about one in every 700 babies. It is a disorder in which an extra chromosome (the number 21 chromosome) is present in the cells of the developing fetus from the time of conception.

Down syndrome usually occurs unexpectedly and about 98% of the time is not inherited. Although Down syndrome occurs more frequently as mothers get older, about 75% of babies with Down syndrome are born to women who are younger than 35.

Down syndrome is always associated with mental retardation, often in the mild to moderate range. Children with Down syndrome have variable but predictable physical characteristics. About 50% have medical problems such as heart defects. Often surgery can correct these defects.

The levels of AFP and estriol in the mother's serum tend to be low while the levels of hCG and inhibin tend to be elevated in pregnancies affected by Down syndrome. Overall, approximately 80% of all pregnancies with Down syndrome will be identified through AFP+ Quad Test. However, detection rates vary with maternal age, ranging from 70% in women under 35 to more than 90% in women 35 and older.
 

What is trisomy 18?

Like Down syndrome, Trisomy 18 is a birth defect caused by the presence of an extra chromosome. Trisomy 18 is much less common than Down syndrome, About one in every 7000 babies will have it. However, like Down syndrome, it usually occurs unexpectedly and the likelihood increases as mothers get older.

Trisomy 18 is a very severe birth defect. Only one in ten babies with trisomy 18 will survive past one year of age. In later months of pregnancy, complications such as fetal growth restriction and fetal death may occur.

The levels of AFP, estriol, and hCG in the mother's serum tend to be low in pregnancies affected with trisomy 18. Approximately 60-80% of all pregnancies affected with trisomy 18 will be identified through AFP+ Quad Testing.

What does it mean if my AFP+ Quad Test result is screen positive?

A positive AFP+ Quad Test means that you are in a higher risk group for having a baby with an open neural tube defect or a chromosome abnormality. However, it does not prove by itself that there is anything wrong with the pregnancy. In fact, only a small number of women with screen positive results will have an abnormal baby. If you have a screen positive result, you should consider specific counseling to discuss further testing.

What are the tests that will be offered if my AFP+ Quad Test is screen positive?

It depends on your particular result. In most cases, after counseling, an ultrasound study (sonogram) will be recommended. Depending on your AFP+ Quad Test result and the results of a sonogram, an amniocentesis or further ultrasound examination may be recommended.
 

What is ultrasound and what will it show?

An ultrasound machine uses sound waves to look at the developing baby. One of the things it can do is check fetal age. Many women will have a “screen positive” AFP+ Quad Test result because the dates of their pregnancies have been misjudged. When this date is adjusted the test result may become screen negative. Occasionally twins will be discovered and will explain the screen positive result.

If the gestational age is correct and you are not carrying twins, either amniocentesis or level II sonography may be suggested. Level II sonography is a detailed examination of the fetus. It cannot be used to diagnose Down syndrome or Trisomy 18 but often can identify Spina Bifida and other fetal abnormalities.

What is amniocentesis and what will it show?

Amniocentesis is a procedure in which the doctor obtains a small sample of fluid that surrounds the developing fetus. The sample is then sent to the laboratory for testing. This fluid sample can be used to diagnose both chromosomal problems such as Down syndrome and Trisomy 18, as well as open neural tube defects such as Spina Bifida. Amniocentesis is an invasive procedure, which means that there is a small risk of miscarriage (less than 1 in 200) associated with it. Results of the test for Down syndrome and Trisomy 18 will take about 7-14 days. Results of the test for Spina Bifida will take about 2-5 days.

What happens if a birth defect is discovered through the AFP+ Quad Test ?

A genetic counselor will be available to discuss your baby's diagnosis in detail and options available to you. One option would be to continue the pregnancy and make arrangements for appropriate medical services at and after delivery. Placing the infant for adoption after birth can also be considered. Another option for you to choose is termination of pregnancy.

If my AFP+ Quad Test is screen negative, does that mean that my baby will be normal?

A screen negative result means that your risk for a child with an open neural tube defect is 1 in 1000 or less. It also means that your risk for a child with Down syndrome is less than that of a 35 year old woman.

It is never possible to be sure that your baby is going to be normal. The AFP+ Quad Test will allow us to identify at least 5 out of 6 cases of open Spina Bifida and almost all cases of anencephaly. It can also lead to the diagnosis of about 8 out of every 10 cases of Down syndrome and Trisomy 18. Remember, a screening test can never completely rule out the possibility of an open neural tube defect, Down syndrome or Trisomy 18. There are also many other birth defects that cannot be identified with this test.

What are the advantages of having the AFP+ Quad Test?

The test may give you and your doctor important information about your pregnancy and your developing baby. Twins may be discovered or your expected date of delivery may be corrected so your prenatal care and visits can be adjusted accordingly.

If your baby is found to have a serious birth defect, you can receive professional counseling about how your child's physical and mental development may be affected. The individual capabilities and potential of children with birth defects are considerations which you may wish to discuss with your counselor or with other healthcare providers. Further information and support are available through groups such as your local Down Syndrome Society and Spina Bifida Association.

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