Alpha-fetoprotein (AFP) is found in both fetal serum and also amniotic fluid. This protein is produced early in gestation by the fetal yolk sac and then later in the liver and gastrointestinal tract. This value is then combined with other markers, as well as the mothers' age and family history to assess a risk for abnormalities.
Estriol is only produced in significant amounts during pregnancy, as it is made by the placenta. If levels of unconjugated estriol are abnormally low in a pregnant woman, this may indicate chromosomal or congenital anomalies like Down syndrome or Edward syndrome.
Human chorionic gonadotropin (hCG) is a hormone produced by a portion of the placenta following implantation. It is used to detect pregnancy, and diagnose and monitor germ cell tumors, as well as gestational trophoblastic diseases. It is combined with other markers to assess fetal disorders in the quad test.
Inhibin is produced in the gonads, pituitary gland, placenta, corpus luteum and other organs. It plays a role in regulating FSH, but when combined with other serological markers, it is useful in screening for fetal disorders and aneuploidies.
There is a high probability of Down syndrome with quad screen results showing low AFP, low estriol, high hCG, and high inhibin A. This can be recalled with "HI," representing high hCG and inhibin A.
There is a high likelihood of Turner syndrome in the fetus with quad screen results showing decreased AFP, decreased estriol, very high hCG, and very high inhibin A. The mnemonic Turner is "very high" represents a very high hCG and inhibin A.
Quad screen results show a very low hCG, low estriol, and low AFP. These results are predictive of Edward syndrome. The mnemonic "Edward is a low HEAP" corresponds with low hCG (H), low estriol (E), and low AFP (AP). Inhibin A is usually normal in Edward syndrome.
Quad screen results showing a normal estriol, normal hCG, normal inhibin A, and normal AFP are indicative of Patau syndrome.
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