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.

In some cases a combination of screening tests is done in the first trimester to look for Down syndrome. This screening test 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). This test is about as accurate as 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 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 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.