Which of the following is not a component of a quad screen?

The quad screen, a maternal blood test performed during the second trimester of pregnancy, is designed to assess the risk of certain fetal conditions, including Down syndrome and neural tube defects. The components of a quad screen specifically include alpha-fetoprotein (AFP), estriol, inhibin A, and human chorionic gonadotropin (hCG).

Alpha-fetoprotein is a protein produced by the fetal liver, and its levels can indicate potential developmental issues. Estriol is an estrogen produced by both the fetus and the placenta; its levels can vary in pregnancies with chromosomal abnormalities. Inhibin A is a hormone produced by the placenta that can also indicate fetal conditions, particularly Down syndrome.

C-reactive protein, on the other hand, is an inflammatory marker used to assess inflammation in the body and does not play a role in the quad screen. It is not included in the assessment of fetal development or in predicting the risk of genetic conditions. Thus, this is why C-reactive protein is the correct answer as it is not a component of the quad screen.