What Does Progesterone Do in the Menstrual Cycle?

During the process of menstruation, progesterone responds to the activity of the ovarian follicles as they prepare to release an egg and causes the uterus to thicken its lining in preparation for a possible pregnancy. Progesterone levels increase during the last two weeks of the menstrual cycle and initiate protein secretion in the endometrium to support a fertilized egg once it is implanted, notes the National Women's Health Resource Center.

The National Women's Health Resource Center explains that many isolated symptoms experienced during a woman's premenstrual course, such as mood swings and localized breast pain, are largely due to the progesterone spikes that occur in her body. If a fertilized egg successfully implants within a woman's uterus and endometrial lining and she becomes pregnant, her body continues to produce high levels of progesterone throughout the duration of her pregnancy. At this point, progesterone and estrogen work together to stop a woman's menstrual cycle while the baby is carried to term.

Women who suffer from irregular periods may have an underlying lack of progesterone production, as it is not present enough in the body to aid in a proper menstrual cycle. In these cases, women can visit with a family doctor or gynecologist to discuss the possibility of using hormone replacement therapy to realign the pituitary gland's hormonal balance, according to the National Women's Health Resource Center.