If you have an abnormal test result:
Click on the links that follow if you have been told that you have an
"abnormal" test result for spina
bifida, Down Syndrome (trisomy 21)
or Trisomy 18.
If you prefer you can view
and print this information as a PDF file (requires Acrobat Reader)
What is this test?
The quad screen is a blood test that measures the levels of certain hormones and
proteins in a pregnant woman’s blood.
Why is this test offered to me?
The purpose of the quad screen is to measure the chance that your baby has one
of three birth defects: neural tube defects, Down syndrome, and trisomy
18.
Will this test find all birth defects?
NO!! Most birth defects are not detected by this or any other test.
What is a neural tube defect?
Neural tube defects are birth defects that affect a baby’s spine or brain.
Spina bifida is an opening along the spine where the bones and skin do not cover
the spinal cord. The effects range from poor control of the legs, leg
paralysis, loss of bowel and bladder control, to severe physical disability and
quadriplegia. About 1 in 1000 babies are born with spina bifida.
Anencephaly is the most severe form of neural tube defect in which the baby’s
brain does not form completely. Babies with anencephaly do not survive.
About 1 in 2000 babies are born with anencephaly. For more information: http://www.sbaa.org/html/sbaa_facts.html
What is Down syndrome?
Down syndrome is the most common genetic form of mental retardation. It is
not inherited, except in rare cases. It is caused when a baby receives an
extra chromosome (package of genetic instructions) from the egg or sperm at the
time of conception. In the case of Down syndrome, the extra chromosome is
always a number 21. Adults with Down syndrome can be mildly or severely
mentally retarded, but most are in the moderate range. Adults with Down
syndrome may have jobs but will rarely be able to live independently.
About 1 in 800 babies are born with Down syndrome. For more information: http://www.ndss.org/aboutds/aboutds.html
What is trisomy 18?
Trisomy 18 is also a chromosome disorder, but the extra chromosome is a number
18. Most babies conceived with trisomy 18 are miscarried or stillborn, but
rarely they can survive years after birth. Children with trisomy 18 often
have birth defects such as clubfeet or heart defects, and are always severely
mentally retarded. About 1 in 5000 babies are born with trisomy 18. For
more information: http://homepages.tig.com.au/~karens/t18.html
How does the test work?
The lab measures AFP, HCG, estriol, and inhibin A in your blood. Only
babies make these proteins and hormones, which pass through the placenta and sac
into their mother’s blood. Your amounts are compared to normal levels to
see whether your levels are normal, high, or low. Using these levels, and
other factors such as your age, your weight, and your race, the lab calculates
the chance your baby has a neural tube defect, Down syndrome, or trisomy 18.
Why would I take this test?
You may want to know during the pregnancy whether your baby has one of these
three birth defects. The quad screen can give you some information
about the health of your baby before birth, without any physical risk to the
baby. If the results are abnormal and follow-up tests diagnose a
birth defect, you can discuss all your options with trained healthcare providers
such as genetic counselors and perinatologists. Some parents decide to end
the pregnancy. For those who continue their pregnancy, knowing the
diagnosis can help them choose the best delivery and treatment plans. This
may improve the short-term and/or the long-term outlook for the child.
Why do some people NOT take the quad screen?
Taking the test itself has no risk to the baby, and the only risk to you is pain
from having your blood drawn. BUT before having this test done, you should
think about whether you want this type of information about your baby.
Getting an abnormal result and deciding whether or not to have more tests causes
most people a lot of stress. If you feel you would never end a pregnancy
under any circumstances, and you do not want to know before birth whether your
baby has a neural tube defect, Down syndrome, or trisomy 18, the quad screen may
not be the right choice for you.
When is the test done?
A common time for the quad screen is between 16 and 18 weeks of pregnancy.
It can be done as early as 15 weeks and as late as 22 weeks.
How long do results take?
Results are usually available within 2-3 days.
Does an abnormal (or “positive”) test result mean the baby has a birth
defect?
NO!! The quad screen cannot diagnose a birth defect. About 1-2%
(1 to 2 in 100) of all women will have a quad screen “positive” for a neural
tube defect; about 5% (5 in 100) of all women will have a quad screen
“positive” for Down syndrome; and about 0.5% (1 in 200) of all women
will have a quad screen “positive” for trisomy 18. Most of these women
will have healthy babies. Abnormal test results ONLY mean that the chance
of one of these three birth defects is higher and that you should be offered
other tests to try to find the cause of the abnormal results. A result of
1 in 100 chance (1%) of Down syndrome from the quad screen means 99 out of 100
times (99%) the baby does NOT have Down syndrome.
What happens next after an abnormal test result?
Most women who have an abnormal quad screen result are referred to specialists,
such as those at Eastside Maternal-Fetal Medicine. The first part of the
visit is spent with a genetic counselor, who spends as much time as needed
answering questions parents have. The genetic counselor reviews the quad
screen results and discusses the follow-up tests available to the parents.
A family and pregnancy history is also taken, to identify other, unrelated,
risks to the baby. Parents then meet with a radiologist or a
perinatologist to do a high-resolution ultrasound. Some parents also
decide to do an amniocentesis.
Does a normal (or “negative”) test result mean the baby does not have
a birth defect?
NO!! Normal test results only mean that the chance of these three birth
defects is not higher than certain levels set by the laboratory. The quad
screen will be “negative” in (it will not detect) about 5-10% of babies with
anencephaly, 20-25% of babies with spina bifida, 20-25% of babies with Down
syndrome, and 20-40% of babies with trisomy 18.
Where can I get more information?
Your healthcare provider may be able to give you more information. Also:
http://www.vtmednet.org/~m145037/vhgi_mem/triple/toc.htm
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