FSH secretion begins to rise in the last few days of the previous menstrual cycle,[3] and is the highest and most important during the first week of the follicular phase[4] (Figure 1).

Under the influence of FSH, aromatase and p450 enzymes are activated, causing the granulosa cells to begin to secrete estrogen.

[4] Throughout the entire follicular phase, rising estrogen levels in the blood stimulates growth of the endometrium and myometrium of the uterus.

[9] It also has a characteristic texture that helps guide sperm through the cervix[10] and to the fallopian tubes, where they wait for ovulation.

[medical citation needed] In addition, basal body temperature may lower slightly under the influence of high estrogen levels.

The short-term drop in steroid hormones between the beginning of the LH surge and the event of ovulation may cause mid-cycle spotting or bleeding.

[13] Follicular waves are best described as the phase when follicles have matured sufficiently and rupture, leading to ovulation.