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.
Human chorionic gonadatropin is a hormone that is produced
by the placenta during pregnancy; a smaller unit
called the beta subunit is elevated in a Down’s syndrome
pregnancy. Blood levels of inhibin A protein are usually
higher in a Down’s syndrome pregnancy.3
A very important consideration in screening test is
the age of the fetus. An ultrasound can also be done
between 10 and 13 weeks to assess the thickness of the
nuchal fold of the developing fetus (nuchal translucency),
which is elevated in chromosomal aneuploidy such as
Down’s syndrome.