Which placental hormone is primarily produced in the first trimester?

• A. hCG
• B. Estrogen
• C. Progesterone
• D. hPL

Answer: (A)

In early pregnancy, the hormone produced primarily by the placenta is human chorionic gonadotropin (hCG). It is made by the placental trophoblast soon after implantation and rises quickly in maternal blood. The key role of hCG in the first trimester is to rescue the corpus luteum from regression, ensuring continued production of progesterone to maintain the uterine lining. While estrogen and progesterone ultimately come from the placenta, their early production is driven by the corpus luteum under the influence of hCG. As gestation progresses, the placenta gradually takes over progesterone and estrogen production, and hPL appears later in the second trimester. hCG levels peak around weeks 8–12 and then decline as placental hormone production becomes sufficient.