Estriol (E3) is the predominant estrogen hormone in the blood and urine of pregnant women.

The majority of circulating estriol is a product of the placental unit, resulting in a precursor (16-α-hydroxy-dehydroepiandrosterone) synthesized in the fetal adrenals and converted into estriol by fetal liver and placenta. The normal production of this hormone is an indicator of placental unit integrity and well-being of the fetus. Most circulating estriol consists of conjugated forms, which are excreted in the urine, free estriol (unconjugated) is present only at a rate of 9%. During normal development of the fetus, estriol production increases progressively, reaching a maximum at 36 weeks of pregnancy.

Sequential monitoring of estriol levels in high risk pregnancies has a higher clinic value than isolated determinations, allowing early therapeutic intervention. Thus persistent low levels of estriol or a sudden reduction of it may be suggestive of fetal distress.

Combined determination of unconjugated estriol, chorionic gonadotropin (HCG total or free-beta HCG) and alpha-fetoprotein (AFP) in the second trimester of pregnancy – investigation known as the triple test – has utility, along with other maternal clinical data in predicting risk of fetal abnormalities at birth.

Recommendations for determination of unconjugated estriol – in the triple test; evaluation of fetal distress and placental function in patients who have complications of pregnancy: preeclampsia, fetal growth retardation, diabetes, Rh isoimmunization, hydatidiform mole and choriocarcinoma.

Method: ELISA.

Reference values

– For the third quarter of pregnancy (fetal distress monitoring) will use these values ​​guide.

Conversion factors: ng / mL x 3.467 = nmol / L; nmol / L x 0.287 = ng / mL.

Interpretation of results:

Low levels of unconjugated estriol (<0.4 MoM) are found in Down syndrome, trisomy 18 and Smith-Lemli-Opitz syndrome. The low levels of estriol are associated with risk: fetal growth retardation, fetal death, preeclampsia, Rh isoimmunization. Lower levels can be seen in anemia, diabetes, malnutrition, liver disease.

Estriol levels may be reduced in the presence of a living fetus anencephaly. Estriol values ​may be increased in fetal hydrops.