- The ‘end product’ of estradiol/estrone metabolism
- 16-OH-E1 can convert into estriol
- Not made in the ovaries
- Very weak estrogen
- Elevated in pregnancy due to placental production
The third estrogen is known as Estriol (E3) and is produced in significant amounts during pregnancy. In men and women, Estriol is irreversibly produced by estradiol (estriol cannot make estradiol) or from estrone through 16-OH-Estrone which makes it the largest circulating estrogen because both Estrone and Estradiol can make it. Despite this, estriol is not nearly as potent as estradiol (Estradiol is 80x more potent!). The least potent of the estrogens, Estriol (E3) levels are traditionally used clinically to gauge the viability of pregnancies. In the context of this profile, estriol is least likely to be associated with high-estrogen problems (e.g. breast cancer), and is generally viewed as a "protective" estrogen. Conversion of 16alpha-hydroxyestrone to estriol is important to consider.
Note: If one is taking a "Bi-Est" or "Tri-Est" preparation, an elevated estriol is not unusual.
Doctors usually test E3 during pregnancy, when it temporarily becomes the main estrogen. Abnormal levels of estriol may be a sign of problems with the baby’s health -- but you’d get a lot more tests to find out for sure. You might need several tests to track changes in your estrogen levels over time.
High estriol implies a potential for elevated 16alpha-hydroxyestrone (16-OH-E1), a very potent estrogen that is associated with increased risk of breast cancer. There appears to be an association of elevated estriol and elevated 16alpha-hydroxyestrone in patients with systemic lupus erythematosus, implying shifted metabolism in that condition.
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