Final answer:
The hormone produced by the placenta to sustain pregnancy and stimulate the ovaries to produce estrogen and progesterone is called human chorionic gonadotropin (hCG).
Step-by-step explanation:
The medical term for the hormone produced by the placenta to sustain pregnancy by stimulating the ovaries to produce estrogen and progesterone is human chorionic gonadotropin (hCG). This hormone is crucial for maintaining the pregnancy especially during its early stages, before the placenta fully takes over the role of the endocrine organ responsible for the production of pregnancy-sustaining hormones. During the initial 7-12 weeks from the last menstrual period (LMP), the corpus luteum is the primary source of pregnancy hormones, but as the placental development occurs and the corpus luteum degenerates around weeks 12-17, the placenta assumes the dominant role in secreting essential hormones such as estrogens, progesterone, and hCG. These hormones work to maintain the pregnancy, prevent new ovarian follicles from developing, suppress uterine contractions, and support maternal and fetal development.