The quadruple screening is triple screening plus measurement of inhibin A. Triple screening includes the measurement of Alpha-fetoprotein (AFP), hCG, and unconjugated estriol (uE3). Quadruple screening increases sensitivity to about 80%, with a 5% false-positive rate, and is usually performed at the second trimester of pregnancy (between 15-20 weeks of gestation). The use of inhibin A in quadruple screening increases both the sensitivity and specificity of the screen. It is a hormone produced by the placenta and normally decreases slightly from 14 to 17 weeks gestation and then rises again. This test is ordered to help evaluate the risk that a fetus has certain abnormalities, including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) and neural tube defects such as spina bifida or a condition called anencephaly. The results of this screening test are combined with the mothers age and ethnicity in order to assess probabilities of potential genetic disorders. In pregnancies where the fetus is carrying the chromosomal defect that results in Down syndrome (trisomy 21), the levels of AFP and unconjugated estriol tend to be LOW and hCG and inhibin A levels are HIGH. See also Prenatal Maternal Triple Screen, Trisomy 21 (Down’s Syndrome), and Trisomy 18 (Edwards Syndrome)