Estriol

**Definition:** A hydroxylated metabolite of ESTRADIOL or ESTRONE that has a hydroxyl group at C3, 16-alpha, and 17-beta position. Estriol is a major urinary estrogen. During PREGNANCY, a large amount of estriol is produced by the PLACENTA. Isomers with inversion of the hydroxyl group or groups are called epiestriol.

**Tree numbers:** - D04.210.500.365.415.331 - D06.472.334.851.437.750

**Synonyms:** - 16-alpha-Hydroxy-Estradiol - 16alpha,17beta-Estriol - (16alpha,17beta)-Estra-1,3,5(10)-Triene-3,16,17-Triol