Hormone Inhibin A
Test OverviewThe inhibin A test is done to measure the amount of this
hormone in a pregnant woman's blood to see if the baby
may have
Down syndrome. Inhibin A is made by the
placenta during pregnancy. The level of
inhibin A in the blood is used in a
maternal serum quadruple screening test. Generally
done between 15 and 20 weeks, this test checks the levels of four substances in
a pregnant woman's blood. The quad screen checks alpha-fetoprotein (AFP), human
chorionic gonadotropin (hCG), a type of estrogen (unconjugated estriol, or
uE3), and the hormone inhibin A. The levels of these substances-along with a
woman's age and other factors-help the doctor estimate the chance that the baby
may have certain problems or birth defects. - Pregnancy: Should I Have Screening Tests for Birth Defects?
Why It Is Done A test for inhibin A is done in
addition to other tests to see if there is a chance of
chromosome problems, such as Down syndrome. How To PrepareYou do not need to do anything before
you have this test. How It Is DoneThe health professional drawing blood
will: - Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
alcohol.
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
blood.
- Remove the band from your arm when enough blood is
collected.
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
bandage.
How It FeelsThe blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch. You may feel anxious while awaiting results of a maternal
serum quad test done to determine the health of your unborn baby. RisksThere is very little chance of a problem from
having a blood sample taken from a vein. - You may get a small bruise at the site. You can lower the chance
of bruising by keeping pressure on the site for several minutes.
- In
rare cases, the vein may become swollen after the blood sample is taken. This
problem is called phlebitis. A warm compress can be used several times a day to
treat this.
ResultsThe inhibin A test is done to measure the
amount of this
hormone in a pregnant woman's blood to see if there is
an increased chance the baby may have
Down syndrome. Inhibin A is made by the
placenta during pregnancy. A normal
result means the level of the hormone inhibin A is low, or negative. An
abnormal result means the level of the hormone inhibin A is high, or positive.footnote 1
The level of the hormone must be reviewed with the quad screen blood tests. All abnormal results will need to be
discussed with your doctor. What Affects the TestThings that may affect your test
results include: - If you smoke. This may increase the level of
inhibin A in the blood.
- If you are
obese. This may decrease the level of inhibin A in the
blood.
The results of the quad screen, including inhibin A, take
into account a woman's age, race, weight, and whether she has
diabetes. What To Think About- The maternal quad screen looks for possible problems in your developing baby (fetus). You can have an ultrasound if
your quad screen is abnormal. If an ultrasound cannot find the cause of the
abnormal results, an amniocentesis may be recommended.
- If abnormal levels of
inhibin A are found, talk with your doctor or a
genetic counselor. The test results can be abnormal,
even when nothing is wrong.
- The level of inhibin A in the blood is often used in a maternal serum quadruple screening test. To learn more, see the topic Triple or Quad Screening for Birth Defects.
ReferencesCitations- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Other Works Consulted- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
- Wapner RJ, et al. (2009). Prenatal diagnosis of congenital disorders. In RK Creasy et al., eds., Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice, 6th ed., pp. 221-274. Philadelphia: Saunders Elsevier.
CreditsByHealthwise Staff
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Kathleen Romito, MD - Family Medicine
Specialist Medical ReviewerSiobhan M. Dolan, MD, MPH - Reproductive Genetics Current as ofMarch 16, 2017 Current as of:
March 16, 2017 Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier. Last modified on: 8 September 2017
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