<P> Estriol, also known as 16α - hydroxyestradiol or as estra - 1, 3, 5 (10) - triene - 3, 16α, 17β - triol, is a naturally occurring estrane steroid with double bonds between the C1 and C2, C3 and C4, and C5 and C10 positions and hydroxyl groups at the C3, C16α, and C17β positions . The name estriol and the abbreviation E3 were derived from the chemical terms estrin (estra - 1, 3, 5 (10) - triene) and triol (three hydroxyl groups). </P> <P> Estriol was discovered in 1930 . It was isolated and purified from the urine of pregnant women by Marrian and colleagues . </P> <P> Estriol can be measured in maternal blood or urine and can be used as a marker of fetal health and well - being . If levels of unconjugated estriol (uE3 or free estriol) are abnormally low in a pregnant woman, this may indicate chromosomal or congenital anomalies like Down syndrome or Edward's syndrome . It is included as part of the triple test and quadruple test for antenatal screening for fetal anomalies . </P> <P> Because many pathological conditions in a pregnant woman can cause deviations in estriol levels, these screenings are often seen as less definitive of fetal - placental health than a nonstress test . Conditions which can create false positives and false negatives in estriol testing for fetal distress include preeclampsia, anemia, and impaired kidney function . </P>

Decreased estriol levels in pregnancy are associated with