An estradiol test measures the level of the hormone estradiol in
the bloodstream. Estradiol plays an important role in sexual
development: It's the most important form of the hormone
estrogen. In sexually mature females, it's produced mainly by
the ovaries, and in smaller amounts by the adrenal glands.
Estrogen is also produced by the placenta during pregnancy.
Sexually mature males have much lower blood levels of estradiol,
which are produced by the testes and adrenal glands. In young
girls, estradiol levels are normally low. As puberty approaches,
usually between ages 8 and 14, the pituitary gland, located just
beneath the brain, secretes two hormones (luteinizing hormone,
or LH; and follicle-stimulating hormone, or FSH) that work
together to stimulate the ovaries to make estradiol. Increased
estradiol production is largely responsible for breast
development, genital growth, and changes in the distribution of
body fat in pubescent girls. Because human sex hormones work so
closely with one another, doctors o