Menstrual Physiology

A menstrual period is the visible endpoint of a cycle controlled by the hypothalamus, pituitary, ovaries, and endometrium. Pulsatile GnRH leads to FSH- and LH-mediated follicular development; ovarian estradiol first builds the endometrium and then, when sustained at a high level, triggers the LH surge and ovulation. Progesterone from the corpus luteum prepares the endometrium for implantation. When the corpus luteum regresses, progesterone and estradiol fall, and the endometrium sheds. For an NP, the cycle is clinical data as well as a reproductive event. The interval between periods, number of bleeding days, perceived volume, pain, and associated symptoms can reveal anovulation, pregnancy, endocrine disease, a structural lesion, a bleeding disorder, or iron deficiency. The first diagnostic fork in a person who could be pregnant is pregnancy exclusion; the first emergency fork in acute bleeding is whether tissue perfusion is threatened.