Early maternal serum screening can include either a
triple screen or quadruple screening test. A triple screen test
involves examining the mother’s blood for 3 items: alphafetaprotein
(AFP), unconjugated estriol (uE3), and human
chorionic gonadotropin (hCG). The quadruple screening
test is a triple screen plus inhibin A.2 Alpha-fetoprotein is
made by the fetal liver and fetal yolk sac. In Down’s syndrome,
the AFP level is decreased in the mother’s blood,
presumably because the yolk sac and fetus are smaller than
normal. Estriol, a hormone produced by the placenta and
the liver, is also decreased in a Down’s syndrome pregnancy.