INSTITUTE FOR FAMILY HEALTH
The Quadruple Screen
What is a Quadruple Screen?
The Quadruple Screen is a blood test done between 15-22 weeks of pregnancy that helps identify
pregnant women at increased risk of certain birth defects.
Will the Quadruple Screen tell me if my baby has a birth defect?
The Quadruple Screen does not test for all birth defects; in fact, no test can. This test screens primarily
for Down syndrome, some neural tube defects, and trisomy 18. Since the Quadruple Screen can only tell
us which babies may be at a higher risk of these birth defects, more tests may be necessary to find out if
your baby truly does or does not have the problem. Also, a negative screen does not guarantee a
completely healthy baby.
What is Down syndrome?
Down syndrome or trisomy 21 is the most common genetic form of mental retardation. It is caused
when a baby has extra genetic material (that is, one extra copy of chromosome number 21 from the egg
or sperm). People with Down syndrome have a distinctive appearance, varying degrees of mental
retardation, poor muscle tone, and a higher frequency of heart defects and other defects. Some adults
with Down syndrome may have jobs, but rarely will be able to live on their own. About 1 out of 800
babies is born with Down syndrome. Even though women who are age 35 or older have a higher risk of
having a baby with Down syndrome, most are born to women under the age of 35. This is because most
pregnant women are younger than age 35.
What is a Neural Tube Defect?
Neural tube defects (NTDs) are birth defects that affect the formation of the spinal cord or brain of the
baby. Spina bifida is one form of NTD where the spinal cord does not form properly and can range
from mild to very severe. Some can be corrected by surgery but severe cases may cause problems with
walking, control with the bladder and bowel, and severe physical disability. Unfortunately, test results
may not be able to tell us the severity of the problem before birth. About 1/1000 babies are born with
spina bifida. The most severe form of NTD is anencephaly where the baby’s brain does not form
completely and he/she cannot survive. Approximately 1/2000 babies are born with anencephaly.
What is Trisomy 18?
Trisomy 18 is a rare disorder affecting about 1/6000 births. Similar to Down syndrome, this is another
chromosomal disorder with an extra copy of chromosome 18. Most pregnancies affected by trisomy 18
are miscarried. Babies born with trisomy 18 have severe mental retardation, heart defects, and other
defects. About ninety percent will die within the first year of life.
How does the Quadruple Screen work?
The blood test measures hormones or markers in the mother’s blood called alpha-fetoprotein (AFP),
human chorionic gonadotropin (hCG), estriol (uE3), and inhibin A (Inh A). Your doctor will gather
information about your medical history and your pregnancy to send to the lab with your blood sample.
Using the information provided, the test is interpreted for your pregnancy’s specific risk of having
particular birth defects. Any incorrect information may lead to misinterpretation of the test results.
What does a negative test result mean?
A negative screen tells us that your baby probably does not have one of the three birth defects described
above and that no further tests are required. However, it cannot guarantee that your baby will not have
some form of birth defect.
What does a positive test result mean?
A positive screen does not diagnose a birth defect. It tells us that your baby has an increased risk of
having one of the three birth defects described above and suggests that follow up tests may be
appropriate. It does not mean that your baby definitely has a problem. In the majority of cases, the baby
is fine. Very few pregnancies that have a positive result will actually have a birth defect. The most
common reasons for a positive screen are that the pregnancy was either farther along or not as far along
as was thought, that there is more than one baby, or due to normal changes in the levels of the markers.
Your doctor or genetic counselor will help you understand the risk and explain any additional tests that
may be recommended.
How good is the Quadruple Screen?
This test detects about 75-80% of Down syndrome, 80-90% of NTDs, and 60% of trisomy 18 cases.
However, about 5-8% of people with normal babies will have a positive screen result, which may lead to
anxiety and an unnecessary testing.
What are reasons to get the Quadruple Screen?
Many people want to know if their baby is at risk of a birth defect ahead of time. If results of the
Quadruple Screen are abnormal and further testing diagnoses a birth defect you can discuss all your
options with a genetic counselor and/or a perinatologist. Some parents may decide to end the
pregnancy. For those who decide to continue their pregnancy, finding out before delivery will give
parents time to prepare and learn more about the baby’s specific problems.
Why do some people NOT get the Quadruple Screen?
Abnormal results and deciding on further testing can cause a lot of stress. Some people don’t want this
type of information about their baby or feel that they would never end a pregnancy under any
circumstances. In these cases, the Quadruple Screen may not be the right choice.
Where can I get more information?
For more information about Down Syndrome: http://www.ndss.org/
For more information about Spina Bifida: http://www.spinabifidaassociation.org/
For more information about Neural Tube Defects: http://www.chg.duke.edu/diseases/ntd.html
For more information about Trisomy 18: http://www.trisomy18support.org/
Disclaimer: This fact sheet is designed to be an informational tool only and is not intended to provide medical advice or replace care by a qualified
medical expert. Permission has been granted for duplication by SouthEast Lancaster Health Services for educational non-profit. Revised with permission
by L. Gort, FNP. Institute for Family Health, 3/2010