Maternal serum screening
Maternal serum screening is a component of fetal screening, which is given to a reproductive female during a pregnancy. Several components (AFP, hCG, and uE3) are measured in the search for absolutely anything that is wrong with the fetus. Combined with maternal age, MSS can have a 60% detection rate of Down's syndrome.
α-fetoprotein (AFP) is a glycoprotein produced by the fetal yolk sac early in development and the gastrointestinal tract and liver later in development. It is the major serum protein of the fetus, with 106 as much AFP in fetal circulation as maternal circulation High AFP levels are associated with NTDs, GI tract abormalities, multiple gestations, incorrect dates, fetal growth restriction and the like. Low AFP is associated with Down's syndrome, gestational trophoblastic disease, incorrect dates, or fetal demise.
Human chorionic gonadotropin (hCG) is also monitored by MSS. It is produced by the trophoblast cells of the placenta. Elevated levels of hCG point to Down's syndrome, while low levels may indicate trisomy 18 or trisomy 13.
Unconjugated estriol (uE3) is produced in the feto-placental unit, and conjugated in the maternal liver. It has a short half-life in maternal circulation. Low unconjugated estriol points to Down's syndrome.