The Four Phases Explained

During the menstrual cycle, simultaneous changes occur in the

  • uterus: endometrium

  • ovary: ovarian follicle and corpus luteum

  • cervix: changes in cervical fluid and sensation

Menstrual Phase

  • the uterus is shedding its lining

  • blood is exiting through the vaginal opening to the vulva

  • the cervix is open to let blood flow

  • estrogen and progesterone are low

Follicular Phase

  • the uterus begins making new lining, entering the early proliferative phase

  • ovarian follicles begin developing in the presence of estrogen

  • cervical fluid production begins developing in the presence of estrogen

  • the fertility window begins

Ovulatory Phase

  • the uterine lining continues to thicken in the late proliferative phase

  • high levels of luteinizing hormone trigger the release of the egg, and ovulation occurs

  • cervical fluid production peaks from the presence of estrogen and LH

  • libido may be increased from a peak in testosterone

Luteal Phase

  • after ovulation, the uterus enters the secretory phase to create the ideal conditions for a fertilized egg

  • the follicle (egg sac) turns into a temporary endocrine organ called the corpus luteum, which secretes progesterone

  • the cervix closes with an impenetrable mucus plug, and cervical fluid dries up