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 often 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), beta human chorionic gonadotropin (beta-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.

In some cases a combination of screening tests is done in the first trimester to look for Down syndrome. It uses an ultrasound measurement of the thickness of the skin at the back of the fetus's neck (nuchal translucency), plus a blood test of the levels of the pregnancy hormone hCG and a protein called pregnancy-associated plasma protein A (PAPP-A). The sensitivity of this screening test is about the same as that of the second-trimester maternal serum quad screening.¹

Should I have the maternal serum screening test (quad screen)?

Health Tools

Health tools help you make wise health decisions or take action to improve your health.

	Decision Points focus on key medical care decisions that are important to many health problems.
	Should I have the maternal serum triple or quadruple test (triple or quad screen)?

Why It Is Done

A test for inhibin A and other chemicals is done to see if chromosome problems, such as Down syndrome, are present.

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 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 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.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

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.

Normal results

Normal results means the level of the hormone inhibin A is low or negative.

Abnormal results

Abnormal results means the level of the hormone inhibin A is above normal or positive.

All abnormal results will need to be discussed with your doctor.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• If you smoke. This increases the level of inhibin A in the blood.
• If you are obese. This decreases the level of inhibin A in the blood.

The results of the quad screen, including inhibin A, are based on a woman's age, race, weight, and whether she is diabetic.

What To Think About

• 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), beta human chorionic gonadotropin (beta-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. For more information about estriol and hCG, see the medical tests Estrogens, Human Chorionic Gonadotropin (hCG), and Alpha-Fetoprotein (AFP) in Blood.
• The maternal quad screen looks for possible problems in your 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. For more information, see the medical test Fetal Ultrasound or Amniocentesis.
• 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.