Proliferative phase thumb|upright=1.6|During the menstrual cycle, levels of estradiol (an estrogen) vary by 200 percent. Levels of progesterone vary by over 1200 percent.
Proliferative phase thumb|upright=1.6|During the menstrual cycle, levels of estradiol (an estrogen) vary by 200 percent Levels of progesterone vary by over 1200 percent.