|
Quadruple screen test
Definition
The quadruple screen test is a blood test done during pregnancy to determine whether the baby is at risk for certain birth defects.
Alternative Names
Quad screen; Multiple marker screening; AFP plus; Triple screen test; AFP maternal; MSAFP; 4-marker screen
How the Test is Performed
This test is usually performed between the 15th and 22nd weeks of the pregnancy, but it is most accurate between the 16th and 18th weeks.
A blood sample is needed. For information on how this is done, see: Venipuncture
The blood sample is sent to a laboratory for testing.
The test measures levels of four pregnancy hormones:
- Alpha-fetoprotein (AFP) – a protein produced by the baby
- Human chorionic gonadotropin (hCG) – a hormone produced in the placenta
- Unconjugated estriol (uE3) – a form of the hormone estrogen produced in the fetus and the placenta
- Inhibin A -- a hormone released by the placenta
If the test does not measure levels of inhibin A, it is called the triple screen test.
To determine the chance of your baby having a birth defect, the test also factors in:
- Your age
- Your ethnic background
- Your weight
- Your baby’s gestational age (measured in weeks from the day of your last period to the current date)
How to Prepare for the Test
No special preparation is necessary.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
The test is done to find out if your baby might be at risk for certain birth defects, such as Down syndrome and birth defects of the spinal column and brain (called neural tube defects).
All pregnant women should be offered this test. The quadruple screen test is normally done some time between the 15th and 22nd week of pregnancy.
Certain women are at greater risk for having a baby with these defects. These women include those over 35 years old during pregnancy, those taking insulin to treat diabetes, and those with a family history of birth defects.
This test is a screening test. This means it does not diagnose birth defects. Instead, it is used to determine whether your baby has a higher risk of these defects.
Normal Results
Normal levels of AFP, hCG, uE3, and inhibin A.
Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
An abnormal test result does NOT mean that your baby definitely has a birth defect. Often, the results can be abnormal if your baby is older or younger than your doctor or nurse had thought.
If you have an abnormal result, you will have another ultrasound to check the age of the developing baby steps.
Further tests and counseling may be recommend if the ultrasound shows a problem. However, some people choose not to have any more tests done, for personal or religious reasons. Possible next steps include:
- Amniocentesis,which checks the AFP level in the amniotic fluid surrounding the baby
- Tests to detect or rule out certain birth defects (such as Down syndrome)
- Genetic counseling
- Ultrasound to check the baby’s brain, spinal cord, kidneys, and heart
During pregnancy, increased levels of AFP may be due to a problem with the developing baby, including:
- Absence of part of the brain and skull (anencephaly)
- Defect in the baby's intestines or other nearby organs (such as duodenal atresia )
- Death of the baby inside the womb (usually results in a miscarriage)
- Spina bifida (spinal defect)
- Tetralogy of Fallot (heart defect)
- Turner syndrome (genetic defect)
High AFP can also mean that you’re carrying more than one baby.
Low levels of AFP and estriol and high levels of hCG and inhibin A may be due to a problem such as:
- Down syndrome (trisomy 21)
- Edwards syndrome (trisomy 18)
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Considerations
The quadruple screen can have false-negative and false-positive results (although it is slightly more accurate than the triple screen). Additional tests are needed to confirm the results.
If the test is abnormal, you may want to talk to a genetic counselor.
References
ACOG Committee on Practice Bulletins. ACOG practice bulletin no. 77: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007;109:217-227.
Anderson CL, Brown CE. Fetal chromosomal abnormalities: Antenatal screening and diagnosis. Am Fam Physician. 2009;79:117-123.
Driscoll DA, Morgan MA, Schulkin J. Screening for Downsyndrome: changing practice of obstetricians. Am J Obstet Gynecol.2009;200:459.e1-459.e9.
Reviewed By: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
