The Inhibin-A test is a quantitative measurement of the level of the hormone inhibin-A in the blood serum of pregnant women. This hormone is primarily produced by the placenta and ovarian cells. During pregnancy, it is used as one of the biomarkers in the triple and quadruple screening tests during the second trimester, as elevated levels are associated with an increased risk of Down syndrome (trisomy 21) and neural tube defects in the fetus.