Progesterone

Progesterone is produced primarily in the ovaries during the luteal (second) phase of the menstrual cycle in the corpus luteum. It plays an important role in regulating the menstrual cycle, preparing the uterus for pregnancy, and maintaining pregnancy in its early stages. Levels fluctuate throughout the different phases of the menstrual cycle and pregnancy, which must be taken into account when interpreting the results.

After ovulation (the release of an egg from the ovary, once a month), progesterone levels in the blood rise significantly because the corpus luteum begins to produce it in increased amounts. This triggers changes in the uterus, preparing it for the implantation of a fertilized egg. If implantation occurs, human chorionic gonadotropin (hCG) begins to be produced, which ensures the preservation of the corpus luteum and the secretion of progesterone from it. If implantation does not occur, the corpus luteum degenerates, progesterone levels in the blood drop rapidly, and menstruation begins within a few days.

After menopause and during childhood, progesterone levels are normally low.

Progesterone is also produced in small amounts by the adrenal glands, but most of it is converted into other hormones; under normal circumstances, this production does not significantly affect blood levels. Additionally, it is produced in the placenta during pregnancy. By the end of the first trimester of pregnancy, the placenta becomes the primary source of progesterone in the blood.

In men, small amounts of progesterone are produced in the testicles.

Serum (blood) progesterone levels are most commonly tested to determine whether ovulation has occurred during the menstrual cycle.

The test may be useful in cases of fertility issues, irregular or abnormal uterine bleeding, to assess placental status in high-risk pregnancies, and in certain adrenal gland disorders.

Elevated progesterone levels may occur in certain ovarian cysts, rare forms of ovarian cancer, adrenal cancer, congenital adrenal hyperplasia, and testicular tumors. They may result from overproduction by the adrenal glands.

Decreased concentrations may occur, for example, in cases of reduced ovarian function, ovulation disorders, missed or absent menstrual bleeding (amenorrhea), ectopic pregnancy, or miscarriage.