PROGESTERONE

Clinical Significance:

Progesterone is one of the steroid hormones. In conjunction with estrogens, it regulates the reproductive tract functions during the menstrual cycle. It is secreted by the corpus luteum and by the placenta and is responsible for preparing the body for pregnancy and, if pregnancy occurs, maintaining it until birth.

Progesterone secretion by the corpus luteum occurs after ovulation:

• Continues the preparation of the endometrium for a possible pregnancy
• Inhibits contraction of the uterus
• inhibits development of a new follicle

If pregnancy does not occur, secretion wanes toward the end of the menstrual cycle, and menstruation begins. If pregnancy does occur, the placenta begins to secrete progesterone, which supplements that of the corpus luteum. In fact, by the fifth month of pregnancy, the placenta secretes sufficient progesterone by itself that the corpus luteum is no longer essential to maintain pregnancy.

Minor sources of Progesterone are the adrenal cortex in men and women and the testes in men. Progesterone levels are low during the follicular phase of the menstrual cycle. After ovulation, progesterone production by the corpus luteum increase rapidly, reaching a maximum concentration 4-7 days after ovulation. During pregnancy, progesterone levels rise steadily to their highest levels in the third trimester.