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 baby'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)?

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Author:	Jan Nissl, RN, BS	Last Updated: October 12, 2006
Medical Review:	Renée M. Crichlow, MD - Family Medicine Adam Husney, MD - Family Medicine Siobhan M. Dolan, MD, MPH - Reproductive Genetics Renee H. Martin, PhD - Medical Genetics
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