Estriol (E₃)

Estriol (E₃) is the predominant estrogen in the blood and urine of pregnant women and is of fetal origin. Normal production serves as a measure of the integrity of the maternal–fetal unit and of fetal well-being.

An E₃ test is performed during pregnancy to evaluate fetal disorders and is part of the maternal triple screen. Declining serial values indicate fetal distress, although in some high-risk pregnancies, E₃ is not reduced. A single determination cannot be interpreted in a meaningful fashion. E₃ is decreased with Down syndrome and with trisomy 18. An elevated serum or unconjugated E₃ above 3 multiples of the gestational age mean, or with an absolute value of >2.1 ng/mL, can indicate pending labor or fetal congenital adrenal hyperplasia.

1. Obtain a 5-mL serum sample by venipuncture using a red-topped tube. Draw the specimen at same time of day on each visit. Observe standard precautions. Label specimen with the patient’s name, date, and test(s) ordered. Record weeks of gestation on the requisition or computer screen. Serial measurements may be recommended to establish a trend.

2. Collect 24-hour urine specimens (E₃: 13–42 mg/24 hr or 46–164 nmol/d) during the third trimester.

1. Decreased E₃ is associated with risk for:

   1. Growth restriction

   2. Fetal death

   3. Fetal anomalies (Down syndrome, fetal encephalopathy)

   4. Fetus past maturity

   5. Preeclampsia

   6. Rh immunization

2. Decreased E₃ also occurs with:

   1. Anemia

   2. Diabetes

   3. Malnutrition

   4. Liver disease

   5. Hemoglobinopathy

Pretest Patient Care

1. Explain test purpose and procedures. Serial testing may be required. See Hormone Testing.

2. No fasting is necessary.

3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Administration of radioactive isotopes within the previous 48 hours interferes with this test.

2. Estrogen or progesterone therapy can interfere with test results.

3. Drugs that can cause decreased levels include vitamins and some phenothiazines.

4. Tetracycline can increase levels.

Normal