The Menstrual Cycle and Related Disorders

The menstrual cycle refers to an orderly progression of events that produces a mature ovum ready for fertilization and an endometrium primed for implantation. Colloquially, the common use of the term menstrual cycle also refers to the periodic shedding of the endometrium that occurs when fertilization and implantation do not occur after ovulation is often termed “menses” by the medical profession and “a period” by the lay public. The tightly orchestrated sequence of events that comprises the menstrual cycle requires appropriate input or drive from the hypothalamic gonadotropin-releasing hormone (GnRH) neuronal network. The decapeptide GnRH is released into the portal circulation in a pulsatile manner, and the pulses must be of sufficient frequency and magnitude to drive pituitary release of the gonadotropins, LH, and FSH. Understanding what is a “normal” menstrual cycle is critical to promoting women’s health, including fertility, and to diagnosing and treating disorders or disturbances of the menstrual cycle, including those commonly associated with infertility and other health consequences. Since there are many medical conditions that cause anovulation and luteal insufficiency, it is imperative that physicians and other health practitioners who care for women as patients understand the physiology of cyclic ovarian function and its impact on women’s health and disease.