What role does progesterone play during pregnancy?

Progesterone plays a crucial role during pregnancy by maintaining the uterine lining, also known as the endometrium. After fertilization, the presence of progesterone is essential for creating a supportive environment for the developing embryo. This hormone is produced primarily by the corpus luteum in the early stages of pregnancy, and later by the placenta once it is fully developed. By maintaining the uterine lining, progesterone ensures that the endometrium remains thick and enriched with blood vessels, providing the necessary nutrients and support for the embryo’s growth and development. This protective function helps to prevent the premature shedding of the uterine lining, which would otherwise lead to miscarriage.

In contrast, the other options do not accurately reflect the role of progesterone during pregnancy. For instance, triggering ovulation and causing menstruation involve the hormonal regulation of the menstrual cycle, where progesterone's primary function comes into play after conception occurs. Additionally, while progesterone can indirectly influence estrogen levels, it does not directly stimulate its release in the context of sustaining a pregnancy.