📖 Definition
The first phase of the menstrual cycle, lasting from day 1 (first day of menstruation) until ovulation. During this phase, FSH stimulates several follicles to develop; as they grow, they produce estrogen, which thickens the uterine lining. The phase ends when one dominant follicle releases its egg at ovulation. Follicular phase length varies; the luteal phase is relatively constant at about 14 days.