Estriol (E3) details

Estriol (E3) is a form of estrogen produced in significant amounts almost exclusively during pregnancy, made by the placenta using precursors supplied partly by the developing fetus. Because its production depends on a functioning fetal-placental unit, estriol has historically been used as part of certain prenatal screening panels (like the quad screen) to help assess risk for specific chromosomal conditions and neural tube defects, typically interpreted together with other markers like AFP and hCG rather than on its own. Outside of pregnancy, estriol has little clinical relevance.