Estriol is a type of estrogen, a hormone that plays a crucial role in the female reproductive system. It is primarily produced during pregnancy by the placenta and is considered one of the three main estrogens, alongside estradiol and estrone. Estriol helps maintain pregnancy and supports fetal development. In addition to its role in pregnancy, estriol is sometimes used in hormone replacement therapy for menopausal women. It is believed to have a milder effect compared to other estrogens, which may reduce the risk of certain side effects. Estriol can also be found in some topical creams for treating vaginal dryness.