Estriol is one of the three main types of estrogen, a group of hormones that plays a key role in female sexual development and function. The other two types of estrogen are estradiol and estrone.
Of the three, estriol is the estrogen that is produced in significant amounts only during pregnancy. It is produced by the placenta, the temporary organ that develops in the uterus during pregnancy to nourish the developing fetus.
The primary role of estriol during pregnancy is thought to be the regulation of the mother’s immune system to prevent the rejection of the fetus. It may also help to prepare the mother’s body for labor and delivery.
Estriol is the weakest of the three estrogens and has the shortest duration of action. It has been investigated for use in treating symptoms of menopause, but as of my knowledge cutoff in September 2021, it was not commonly used for this purpose.
Like all hormones, maintaining the right balance of estriol in the body is important for health. However, because it’s primarily produced during pregnancy, issues with estriol levels are usually related to pregnancy health. For example, abnormally low or high levels of estriol during pregnancy can indicate potential issues with the fetus’s development.