Progesterone is produced by the ovarian corpus luteum and the adrenal glands. It has no biological function in men, whereas in women, it prepares the uterus for the embryo. Progesterone levels are low at the beginning of the menstrual cycle and increase at the time of ovulation. The corpus luteum continues to produce progesterone for a few days and then stops. If the fertilized egg is properly implanted, the placenta takes over and produces progesterone throughout the pregnancy. If there is no implantation, progesterone levels drop, triggering menstruation.
Progesterone levels are interpreted based on the phase of the menstrual cycle (infertility assessment) and other reasons for testing (follow-up in early pregnancy, abnormal uterine bleeding, etc.). FSH, LH and estradiol levels generally accompany progesterone measurements.
Progesterone levels that do not show an increase/decrease sequence during the menstrual cycle signal an absence of ovulation. If levels do not gradually rise in early pregnancy, there is a risk of ectopic pregnancy or miscarriage. Abnormally high levels can sometimes be seen in ovarian cysts or overactive adrenal glands (women and men).