Questions: Which class of antibody crosses the placenta in pregnant people?

The answer is the fourth one (d): IgG.

Explanation for each option:

a. IgM: This antibody is the first to be produced in response to an infection, but it does not cross the placenta due to its large size.

b. IgA: This antibody is primarily found in mucosal areas and secretions like saliva and breast milk, but it does not cross the placenta.

c. IgE: This antibody is associated with allergic reactions and does not cross the placenta.

d. IgG: This is the only class of antibody that can cross the placenta. It provides passive immunity to the fetus by transferring maternal antibodies, which help protect the newborn against infections during the early months of life.

In summary, IgG is the class of antibody that crosses the placenta in pregnant people.