- 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.
References:
https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/81711
Estriol (FMV urine, menopause)
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