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Estriol Blood Test: High & Low Levels + Normal Range

Written by Biljana Novkovic, PhD | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Biljana Novkovic, PhD | Last updated:

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Estriol is one of the three main estrogens. However, it’s levels are usually so low they can’t be detected in the blood. They play a major role in pregnancy. Learn what low or high estriol levels mean here.

What is Estriol?

The three main estrogens in the body are estrone (E1), estradiol (E2), and estriol (E3). This test measures the amount of estriol in your blood.

In women, estriol is produced in the ovarian follicles and corpus luteum. Estrone and estradiol can also be converted into estriol [1, 2, 3].

Normally, in both men and women, estriol levels are the lowest compared to the other two estrogens and cannot be detected in the blood (serum) [4, 1].

Estriol levels increase during pregnancy. After the third semester, the placenta converts DHEA-S into estriol and other estrogens. Estriol becomes the major estrogen, peaking during the third trimester. After a woman gives birth, her estriol levels will decrease and go back to normal [4, 1].

Estriol Tests

Estriol tests are used to monitor high-risk pregnancies and screen for problems with the fetus [5].

Estriol can be measured in the blood or in saliva. The advantage of saliva tests over blood tests, is that saliva tests actually measure the amount of free hormones, while in blood these hormones are mostly bound to proteins (SHBG and albumin) [6, 7, 8].

In addition, a saliva test is easy to do and noninvasive.

On the other hand, accurate measurement of hormones in the saliva depends on proper sample collection and proper analyses [9]. It makes sense to repeat the test or do a blood hormone test to confirm any abnormal findings [9].

Normal Range of Estriol

Quest provides the following ranges:

Adult Male ≤0.18 ng/mL
Adult Female (Non-pregnant) ≤0.21 ng/mL
First trimester ≤2.50 ng/mL
Second trimester ≤9.60 ng/mL
Third trimester ≤14.60 ng/mL

Labcorp provides the following ranges in pregnancy:

Gestational Week Median Central 95% Range
27 4.6 2.6 − 7.1
28 4.7 2.6 − 7.8
29 5.0 2.6 − 8.6
30 5.5 2.7 − 9.6
31 6.1 2.9 − 11.0
32 6.9 3.2 − 12.7
33 8.0 3.4 − >13.3
34 9.3 3.7 − >13.3
35 11.3 4.3 − >13.3
36 >13.3 5.3 − >13.3
37 >13.3 6.2 − >13.3
38 >13.3 7.4 − >13.3
39 >13.3 8.1 − >13.3
40 >13.3 8.5 − >13.3

Levels can vary between labs, depending on techniques, equipment, and chemicals used. In addition, levels vary from day-to-day.

Saliva tests are still in development and aren’t standardized. Levels will depend on the laboratory doing the testing.

Low Estriol

Causes listed below are commonly associated with low estriol levels. Work with your doctor or another health care professional to get an accurate diagnosis. Your doctor will interpret your result, taking into account your medical history, symptoms, and other test results.

A result that’s lower than normal, doesn’t necessarily mean that you have a health condition needing treatment.

In pregnant women, low estriol levels may be caused by issues such as:

  • The inability of the adrenal glands to produce enough hormones (adrenal insufficiency) [10]
  • Steroid sulfatase deficiency [11, 10]

Some drugs can also lower estriol levels:

  • Corticosteroids [12]
  • Propylthiouracil, a drug used to treat Grave’s disease and overactive thyroid gland (hyperthyroidism) [12]

Having low levels are associated with a higher risk of pregnancy complications, trisomies (Down’s syndrome) [13, 14, 15, 5, 16].

Low levels of uE3 also have been associated with pregnancy loss, Smith-Lemli-Opitz syndrome (defect in cholesterol biosynthesis), X-linked ichthyosis and contiguous gene syndrome (placental sulfatase deficiency disorders), aromatase deficiency, and primary or secondary fetal adrenal insufficiency.

Increasing Estriol

It’s important to work with your doctor to find out what’s causing your low estriol and to treat any underlying conditions!

The additional lifestyle changes listed below are other things you may want to discuss with your doctor. None of these strategies should ever be done in place of what your doctor recommends or prescribes!

Since estriol can be derived from other estrogens, increasing your estrone and estradiol levels may help increase estriol levels, but these may not work depending on the underlying health issue [3].

High Estriol

Causes listed below are commonly associated with high estriol levels. Work with your doctor or another health care professional to get an accurate diagnosis. Your doctor will interpret your result, taking into account your medical history, symptoms, and other test results.

A result that’s lower than normal, doesn’t necessarily mean that you have a health condition needing treatment.

In women, the most common cause of high estriol levels is pregnancy [17].

If you are pregnant, optimal estriol values will depend on the gestational week. Check your lab ranges and consult your doctor for more information.

About the Author

Biljana Novkovic

Biljana Novkovic

Biljana received her PhD from Hokkaido University.
Before joining SelfHacked, she was a research scientist with extensive field and laboratory experience. She spent 4 years reviewing the scientific literature on supplements, lab tests and other areas of health sciences. She is passionate about releasing the most accurate science and health information available on topics, and she's meticulous when writing and reviewing articles to make sure the science is sound. She believes that SelfHacked has the best science that is also layperson-friendly on the web.

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