Determining Your Baby’s Risk of Birth Defects

What is maternal serum screening?

The maternal serum multiple marker test is a prenatal screening test using blood from the mother that can help identify women who may be carrying a baby with certain types of birth defects (such as neural tube defects, Down syndrome, and trisomy 18 syndrome).

This test should be offered to all pregnant women regardless of age. Maternal serum screening is available to any pregnant woman between 15 and 21 weeks of pregnancy (counting from the first day of the last menstrual period). Women 35 years of age or older should be offered other diagnostic testing such as amniocentesis.

This blood test provides information about your developing baby. The maternal serum multiple marker test measures at least three markers found in the mother’s blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG) and unconjugated estriol. These substances are made by the developing baby and the placenta. The levels of these markers can be analyzed through a simple blood sample. Certain birth defects can sometimes be detected when the levels of these markers are different than expected. Some laboratories will measure additional chemicals to achieve a higher detection rate for these conditions.

What does an abnormal test mean?

Maternal serum multiple marker screening is not a diagnostic test, but a screening test. A positive or abnormal result indicates the need for additional testing, such as ultrasound or amniocentesis. An abnormal test does not necessarily mean there is a definite health problem with the pregnancy. Genetic counseling to discuss this test is recommended.

Elevations in AFP may –

• identify a high percentage of neural tube defects including anencephaly;
• detect a miscalculated due date;
• identify twins or a pregnancy with multiples;
• detect an abnormal opening in the abdominal wall;
• predict risk for preterm delivery;
• determine a low birth weight; or
• represent a normal variation.

Neural Tube Defects
There are two main types of neural tube defects: Anencephaly occurs when development of the skull is incomplete. Babies born with anencephaly may be stillborn or die soon after birth. Spina bifida is an incomplete closure of the spine. Babies born with spina bifida may have medical problems involving weakness or paralysis of the legs, problems with bowel and bladder control, chronic infection and, rarely, mental retardation.

It is also known that some pregnancies that result in a baby with Down syndrome can be identified when a particular pattern or combination is noticed in the levels of all of the screened substances.

Down Syndrome
Down syndrome is a genetic condition that results in mental retardation, medical problems such as heart conditions, and characteristic facial features. Down syndrome is also known as trisomy 21 which means there is an extra chromosome 21. It occurs in approximately 1 in 700 births and can occur in infants born to women of any age or race, even if there is no family history of Down syndrome. However, the risk for Down syndrome does increase with maternal age.

Another chromosomal disorder known as trisomy 18 may be identified with the screening when the AFP levels are lower than expected.

Trisomy 18 Syndrome
Trisomy 18 syndrome is a genetic condition in which the baby has an extra chromosome 18; it affects 1 out of 8,000 births. The syndrome is characterized by specific abnormal features and organ malformations. Few infants with this syndrome survive beyond the first year of life.

How accurate are these tests?

The maternal serum multiple marker test is able to identify –

• 80 percent to 85 percent of developing babies with neural tube defects.
  
  
• 60 percent to 70 percent of developing babies with Down syndrome when the mothers are younger than 35 years of age.
  
  
• 80 percent to 90 percent of developing babies with Down syndrome when the mothers are older than 35 years of age.
  
  
• 60 percent to 80 percent of developing babies with trisomy 18 syndrome.
  
  
• 75 percent of developing babies with abdominal wall problems.

Important Facts

Maternal serum multiple marker test is sometimes called triple test, AFP plus, enhanced AFP, AFP3 test or triple screen prenatal risk profile (PRP). More recently, blood is being tested for four markers and the test may be called the quad screen or AFP4, etc.

• The test is a simple blood test on the mother’s blood and poses no threat to the mother or to her baby.
  
  
• This is a voluntary test. If you have any questions about the test, you should discuss them with your physician.
  
  
• Although the test can detect some common health conditions, a normal result does not guarantee a healthy baby.
  
  
• An abnormal test does NOT always mean there is a problem with the baby. It simply means that other tests may be suggested.
  
  
• Abnormal results are usually followed by other diagnostic tests, including high resolution ultrasound or amniocentesis.
  
  
• The results of this test help to give you and your physician the knowledge to provide the best care and preparation that you need for the birth of your baby.

For more information, please contact Illinois Department of Public Health 535 W. Jefferson, 2nd Floor Springfield, IL 62761 217-785-8101 TTY (hearing impaired use only) 800-547-0466

Illinois Department of Public Health 535 West Jefferson Street Springfield, Illinois 62761 Phone 217-782-4977 Fax 217-782-3987 TTY 800-547-0466 Questions or Comments