Estradiol (Estrogen) is a female hormone, produced primarily in the ovary. The amount of estrogen produced depends on the phase of the menstrual cycle.
Men also produce estradiol, but only very small amounts.
Shortly before ovulation, estradiol levels surge and then fall immediately after ovulation. They then rise again and remain elevated until 2-3 days before menstruation.
If pregnancy occurs, the estradiol levels remain elevated.
If pregnancy does not occur, then estradiol levels fall, which, in combination with falling progesterone levels, provoke a menstrual flow.
*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.