Quad screen test in pregnancy
The quad screening test is a
maternal blood screening test that looks for four specific substances: AFP,
hCG, estriol, and inhibin-A.
- AFP: alpha-fetoprotein is a protein produced by the fetus.
- HCG: Human chorionic gonadotropin is a hormone produced by the placenta.
- Estriol: Estriol is an estrogen produced by both the fetus and the placenta.
- Inhibin-A: Inhibin-A is a protein produced by the placenta and ovaries.
The quad screening
test is a maternal blood screening test similar to the triple screening test.
However, the quad screen does not only look for the three specific substances
assessed in these tests (AFP, hCG, and estriol), but also a fourth substance
known as inhibin-A.
Screening is essentially the
same as screening tests that look for only three substances, except that
pregnancies at risk of Down syndrome are more likely to be detected due to the
assessment of inhibin-A levels. The false positive rate of the test is also
lower.
What is a screening test?
It is very important to
remember what a screening test is before you do it. This will help reduce the
anxiety that may accompany the test results. Screening tests are not limited to
blood test results. They compare a number of different factors (including age,
ethnicity, blood test results) and then evaluate a person's chances of having
an anomaly.
These tests do NOT diagnose
the problem; they only signal that further testing is needed.
How is the quad screen test done?
The quad test involves drawing
blood from the mother, which takes 5 to 10 minutes. The blood sample is then
sent to a laboratory for analysis. The results usually take a few days.
What are the risks and side
effects for the mother or baby?
Other than discomfort when
drawing blood, there are no known risks or side effects associated with the
Quad Screen test.
When is the quad screen test done?
A quad screening test is
performed between the 16th and 18th weeks of pregnancy.
All pregnant women should be
offered a quad screening test, but it is recommended for women who:
- Have a family history of birth defects
- Are 35 years or older
- Used possible harmful medications or drugs during pregnancy
- Have diabetes and use insulin
- Had a viral infection during pregnancy
- Have been exposed to high levels of radiation
What is the quad screen test looking
for?
The square screen measures
high and low levels of AFP, abnormal levels of hCG and estriol, and high levels
of inhibin-A. The results are combined with the age and ethnicity of the mother
to assess the likelihood of potential genetic disorders. A high level of AFP
may indicate that a developing child has a neural tube defect such as spinabifida or anencephaly.
However, the most common cause
of high AFP levels is inaccurate timing of pregnancy.
Low levels of
alpha-fetoprotein and abnormal levels of hCG and estriol may indicate that the
developing baby has trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome),
or another type of chromosomal abnormality.
What do the quad-screen results mean?
It is important to remember
that quad screening is a screening test and not a diagnostic test. This test
only notes that the mother is at risk of carrying a child with a genetic
disease. Many women who receive an abnormal test result give birth to healthy children.
Abnormal test results require further testing to make a diagnosis.
A more conservative approach
is to perform a second quad screening test followed by high definition
ultrasound. If the test continues to show abnormal results, a more invasive
procedure, such as an amniocentesis, may be performed.
Any invasive procedure should
be carefully discussed with your doctor and between you and your partner.
What are the reasons for additional testing?
Square screening is routine
screening with no known risk to mother or baby. Quad screen results may require
additional testing. The reasons why further testing should be done vary from
person to person and couple to couple.
Performing additional tests
allows you to confirm the diagnosis, and then opens up certain possibilities
for you:
- Pursue potential interventions that may exist (fetal surgery for spina bifida)
- Begin planning for a child with special needs
- Start addressing anticipated lifestyle changes
- Identify support groups and resources
- Make a decision about carrying the child to term
Some individuals or couples
may refuse to be tested or additional tested for a number of reasons:
- They are satisfied with the results, regardless of the outcome
- For personal, moral or religious reasons, deciding to carry a child to term is not an option.
- Some parents choose not to allow tests that could harm a developing child.