The main phases of menstrual cycle are menstruation, follicular phase, ovulatory phase and luteal phase.

Phase is followed by follicular phase. During this stage primary follicles in the ovary grow to become a fully mature graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and uterus are induced by changes in the levels of pituitary and ovarian hormone.

The hormones ($LH$ $\&$ $FSH$) increases during the follicular phase and stimulates follicular development as well as secretion of estrogens by the growing follicles.

Both $LH$ and $FSH$ attain a peak level in the middle of cycle (about $14$th day). Rapid secretion of $LH$ leading to the maximum level during the mid cycle and induces rapture of graafian follicle and there by the release of ovum ovulation.