**Question:** Triple test of Down's syndrome includes following except-

A. Serum beta human chorionic gonadotropin (β-hCG)
B. Serum alpha-fetoprotein (AFP)
C. Serum estriol
D. Serum inhibin A

**Correct Answer:** D. Serum inhibin A

**Core Concept:** Down's syndrome is a genetic disorder caused by the presence of an extra chromosome 21. This leads to characteristic features such as intellectual disability, facial abnormalities, and increased risk of certain medical conditions, including congenital heart defects and thyroid dysfunction. The triple test is a screening test used to assess the risk of Down's syndrome in pregnant women. The test measures three specific proteins in a woman's blood:

**Why the Correct Answer is Right:** Serum inhibin A is not included in the triple test for Down's syndrome because it is primarily involved in the regulation of sperm production in men and is not directly related to the development of Down's syndrome or fetal abnormalities. The triple test primarily focuses on measuring proteins that reflect fetal aneuploidy (abnormal number of chromosomes) and fetal abnormalities.

**Why Each Wrong Option is Incorrect:**

A. Serum β-hCG (human chorionic gonadotropin) is involved in the production of placental hormones and is elevated in pregnancy. It is included in the triple test as it can help differentiate between Down's syndrome and other types of aneuploidy, such as trisomy 18 and trisomy 13.

B. Serum AFP (alpha-fetoprotein) is a protein produced by the liver and yolk sac during fetal development. It is elevated in Down's syndrome cases and is included in the triple test as it helps to detect other types of aneuploidy and fetal abnormalities.

C. Serum estriol is a type of estrogen produced by the fetal adrenal glands and placenta. It is elevated in certain pregnancy complications and Down's syndrome, but is not specifically included in the triple test.

**Clinical Pearl:** The triple test screening test helps to assess the risk of Down's syndrome and other chromosomal abnormalities in pregnant women. It is usually performed between 15 and 20 weeks of gestation. If the results indicate a high risk, a more detailed test, such as chorionic villus sampling (CVS) or amniocentesis, may be considered to confirm the diagnosis. In general, the triple test has a sensitivity of 85-90% and a specificity of 97-98%, making it useful for ruling out the condition rather than confirming it.