In the body, estrogen has several functions. It aids in the maturation of a woman's reproductive organs. It helps her keep her feminine features, such as breasts and pubic hair. Estrogen is one of the two sex hormones generally associated with cisgender women, transgender males, and nonbinary persons with vaginas - everyone who was assigned female at birth (AFAB). Fertility (the capacity to conceive), pregnancy health, menstrual cycle health, and other medical issues can all be better understood with the testing of estrogen levels.