01 · Cycle basics
What is a menstrual cycle?
FSH · LH · estrogen · progesterone
Most people begin menstruating around ages 11 to 14 and continue until menopause around ages 48 to 55. Cycles usually run about 28 to 30 days, with bleed lasting 3 to 7 days.
The cycle is regulated by follicle-stimulating hormone (FSH), luteinising hormone (LH), estrogen, and progesterone in a delicate balance. At puberty, the hypothalamus signals the pituitary to release FSH and LH. Those hormones drive estrogen and progesterone shifts for ovulation and the uterine lining. If fertilisation does not occur, estrogen and progesterone fall, the endometrium sheds, and another cycle begins.