Estriol

Used to evaluate fetal distress and placental function in the management of patients facing complications such as preeclampsia, fetal growth retardation, diabetes, Rh immunization, choriocarcinoma and hydatidiform mole. May be elevated in hydrops fetalis in the presence of a dying fetus. May be low in the presence of a living anencephalic fetus.

Estriol, E3, is synthesized in the placenta from 16–hydroxydehydroepiandrosterone of fetal origin. Thus, normal production can serve as a measure of the integrity of the fetoplacental unit. Sequential monitoring of estriol in high risk pregnancy has made possible early intervention and fetal salvage. Chronically low estriol values are found in intrauterine growth retardation but also are sometimes seen in normal pregnancy. A decreasing trend is indicative of fetal distress. The sensitivity and specificity of this test for detecting fetal distress are very poor; thus its use for this purpose has been largely abandoned.

Combined evaluation of unconjugated serum estriol, maternal serum hCG, maternal serum AFP, and maternal age has value in predicting risk for fetal chromosomal abnormalities during pregnancy. The use of maternal serum AFP, hCG, and estriol predicts 65% of Down syndrome, as opposed to 28% if only serum AFP is used.3,4,5

Limitations: Single values are almost impossible to interpret; trends in a series of measurements are much more important. May be low in case of placental sulfatase deficiency in the presence of a healthy baby. Other causes of decreased estriol levels include subjects living at high altitudes, anemia, severe liver disease, and a variety of drugs. Estriol may be increased with multiple pregnancy and with oxytocin. It is not reliable in the presence of renal disease.