Which hormone is primarily responsible for the development of the placenta?

Human chorionic gonadotropin (hCG) is the hormone primarily responsible for the early development and maintenance of the placenta during pregnancy. After a fertilized egg implants in the uterus, hCG is secreted by the developing placenta. This hormone plays a crucial role in signaling the corpus luteum to continue producing progesterone, which is essential for maintaining the uterine lining and supporting the pregnancy.

hCG levels rise significantly in early pregnancy and are the basis for most home pregnancy tests. By promoting the continued production of progesterone, hCG helps ensure that the uterine environment remains stable for the developing embryo, thereby supporting the growth and development of the placenta itself.

While estrogen and progesterone are essential for various aspects of pregnancy and fetal development, including the overall maintenance of the pregnancy and the development of secondary sex characteristics, they are not primarily responsible for the formation of the placenta itself. Luteinizing hormone (LH) is involved in the menstrual cycle and ovulation but does not play a direct role in placental development. Hence, hCG's specific function in supporting the early stages of pregnancy makes it the key hormone associated with placental development.