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The menstrual cycle is divided into two phases--the follicular or proliferative phase; and the luteal or ovulatory phase. The follicular phase includes the time when menstruation occurs and is followed by proliferation or the growth and thickening of the endometrium. This phase typically lasts from 10-14 days, starting with the first day of menstruation.
Estrogen and progesterone levels are at their lowest during menstruation. When bleeding stops, the proliferative phase begins causing the endometrium to grow and thicken in preparation for pregnancy. During the next (approximately) two weeks, FSH levels rise causing maturation of several ovarian follicles and the size of the eggs triple.
FSH also signals the ovaries to begin producing estrogen which stimulates LH levels until around day 14 of your cycle when one of the follicles bursts, and the largest egg is released into one of the fallopian tubes.
This phase is followed by the premenstrual phase, known as the luteal phase. This premenstrual period lasts approximately 14 days. After ovulation, LH causes the corpus leuteum to develop from the ruptured follicle. The corpus leuteum produces progesterone.
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