estradiol
Meaning of estradiol: A blood estradiol result means little without knowing where in the cycle, or where in life, the sample was taken.
Definition of estradiol
Estradiol is the most potent naturally occurring estrogen and the main one produced by the ovaries during the reproductive years. It is a steroid hormone built from cholesterol, and it drives the menstrual cycle, maintains reproductive tissue and helps preserve bone. Smaller amounts are made by the testes, the adrenal glands and fat tissue.
How do the three estrogens differ?
| Form | Strength | When it predominates |
|---|---|---|
| Estradiol | The most potent | The reproductive years, made chiefly by the ovaries |
| Estrone | Weaker | After menopause, made largely in fat tissue from adrenal precursors |
| Estriol | Weakest | Pregnancy, produced in quantity by the placenta |
All three are estrogen, and all act on the same receptors, so the difference lies in potency and in which one is abundant at a given stage of life.
How do levels change over a lifetime?
Levels are low before puberty, rise as the ovaries begin to function, and then swing through each menstrual cycle: climbing as a follicle matures, peaking just before the egg is released, dipping, then rising again more modestly in the second half. In pregnancy they climb far higher than at any other time. At menopause the ovaries stop responding and estradiol falls steeply, after which estrone becomes the dominant form. In men the enzyme aromatase converts testosterone to estradiol, and the small amount produced matters for bone strength and for sperm production.
Why is it measured, and where is it used as a medicine?
A blood level is checked when menstrual periods are irregular or absent, when puberty arrives unusually early or late, during fertility treatment to track how follicles are responding, and where premature ovarian insufficiency is suspected. The result is meaningless without the cycle day or menopausal status attached, since the same figure can be normal at one point and clearly abnormal at another. As a medicine, estradiol appears in menopausal hormone therapy, in gender-affirming hormone therapy and in some contraceptives. It is broken down heavily by the liver when swallowed, which is why patches, gels, sprays, vaginal preparations and injections all exist alongside tablets.
Also known as
Used in a sentence
A blood test measured the patient's estradiol level as part of the fertility evaluation.
Good to know
An estradiol level is interpreted against the phase of the menstrual cycle or menopausal status, since a value that is ordinary at one point in the cycle can look clearly abnormal at another.
Word origin
Where “estradiol” comes from
Formed from estrus, from Greek oistros, meaning frenzy or gadfly, with -di-, meaning two, and -ol, marking the pair of hydroxyl groups in its structure.