What hormone does the placenta primarily produce during pregnancy to maintain the corpus luteum?

The hormone primarily produced by the placenta during pregnancy to maintain the corpus luteum is human chorionic gonadotropin (hCG). Shortly after implantation of the embryo into the uterine lining, the placenta begins to secrete hCG. This hormone plays a critical role in signaling the corpus luteum to continue its production of progesterone, which is essential for maintaining the uterine lining and supporting the early stages of pregnancy.

The corpus luteum is responsible for producing progesterone during the first trimester until the placenta takes over this role. The presence of hCG in the bloodstream is also what pregnancy tests detect, making it an important marker for confirming pregnancy. Thus, hCG not only maintains the corpus luteum but is also vital for the continuation of pregnancy during its early phases.