Total estrogens comprise the total quantity of estrone, estradiol, and estriol. The estrogens are involved in the development of female sex organs and secondary sex characteristics. Before the ovum is fertilized the main action of the estrogens is on the growth and function of the reproductive tract to prepare it for the fertilized ovum.
During the follicular phase of the menstrual cycle the total estrogens level shows a slight increase. The production of total estrogens then increases markedly to peak at around day 13. The peak is of short duration and by day 16 of the cycle levels will be low. A second peak occurs at around day 21 of the cycle; if fertilization does not occur, the production of total estrogens decreases.
In post-menopausal women the concentration of all estrogens decreases substantially and estrone becomes the predominant estrogen. In pregnant women the concentration of all estrogens escalates and estriol becomes the predominant estrogen.