<prompt> Naturally occuring estrogens are:a Estroneb Estrad iolc Estriold Diethylstilbesterole Pregnanediolabbcabcbcd  <response>: Natural estrogens are C18 steroidsMain Source - Theca and granulosa cells of Graafian follicle and corpus luteum.Secondary source - Adrenal cortexNaturally occurring estrogenEstradioI Main estrogen during reproductive years,Estrone Produced by peripheral aromatization of androstenedione - Main estrogen after menopauseEstriol the main source is placenta - Main estrogen during pregnancy. It is a marker of feto-maternal-placental well being. 