Unconjugated estriol is a form of the estrogen hormone primarily produced by the placenta during pregnancy. It plays a crucial role in fetal development and is often measured to assess the health of the pregnancy. Low levels of unconjugated estriol may indicate potential complications, while higher levels are typically associated with a healthy pregnancy. This hormone is also used in certain medical evaluations, such as assessing ovarian function and diagnosing conditions related to estrogen imbalance.