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Hormone Inhibin A

Test Overview

The 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.

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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 Prepare

You do not need to do anything before you have this test.

How It Is Done

The 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 Feels

The 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.

Risks

There 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.

Results

The 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 1The 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 Test

Things 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.

References

Citations

  1. 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.

Credits

ByHealthwise Staff
Primary Medical Reviewer Sarah A. Marshall, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Kathleen Romito, MD - Family Medicine
Siobhan M. Dolan, MD, MPH - Reproductive Genetics

Current as ofNovember 21, 2017

Current as of: November 21, 2017

Author: Healthwise Staff

Medical Review: Sarah A. Marshall, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics