Progesterone is a hormone produced by the ovaries in women and, to a lesser extent, by the adrenal glands. It plays an important role in regulating menstrual cycles and maintaining pregnancy. Progesterone levels fluctuate throughout the monthly cycle and during pregnancy.
During the first half of the menstrual cycle (the follicular phase), progesterone levels are relatively low, stimulating the growth of a new egg-producing follicle. As the egg matures, its production of estrogen increases, which causes a surge in luteinizing hormone (LH) that triggers ovulation. After ovulation, the remnants of the ruptured follicle form the corpus luteum, which produces progesterone to prepare the uterus for implantation of a fertilized egg.
If fertilization occurs, the embryo will produce human chorionic gonadotropin (hCG), which maintains the corpus luteum and its production of progesterone. This helps support the early stages of pregnancy until the placenta takes over hormone production.
Progesterone levels are often measured in fertility treatments, prenatal care, or during menstrual cycle irregularities to help diagnose and manage conditions related to reproductive health.