Estriol

What is estriol?

Estriol is one of three estrogen hormones. Estriol levels rise throughout pregnancy, helping to keep the fetus and your uterus healthy. The levels are at their highest right before childbirth.

Everyone makes estriol. But in people who aren’t pregnant, the levels are almost undetectable. Other names for estriol include oestriol and E3.

What does estriol do?

Unlike other estrogen hormones, estriol only has a significant role in pregnancy. During pregnancy, estriol:

• Helps your uterus grow as the fetus gets bigger
• Makes your body more sensitive to other pregnancy hormones
• Prepares your body for labor and delivery and breastfeeding

Estriol levels start to rise around the eighth week of pregnancy. They continue to increase throughout pregnancy. Estriol levels are at their highest about three weeks before you give birth. Some researchers believe that rising estriol levels may play a role in preparing your body for labor. But they don’t fully understand this connection.

Estriol as medication

There’s also a laboratory-made form of estriol (a bioidentical hormone). Healthcare providers may prescribe it as part of hormone therapy for menopause.

The use of this medication for the treatment of menopausal symptoms isn’t FDA-approved in the United States. It’s usually only available at compounding pharmacies. Please consult your healthcare provider before using compounded estriol.

Researchers are exploring the many possible functions of estriol. Lab-made estriol may also:

• Improve brain (cognitive) function
• Relieve menstrual migraines
• Smooth wrinkles
• Treat nervous system disorders that cause inflammation, like multiple sclerosis (MS)
• Treat postpartum depression

These uses are considered off-label and are still being researched. Please talk to your provider before using estriol for any of these purposes.

Where does estriol come from?

The placenta is mainly in charge of making estriol. But there are a few steps to the process:

1. The fetus’s adrenal glands make a hormone called dehydroepiandrosterone sulfate (DHEAS).
2. The fetus’s liver changes DHEAS into another chemical called 16a-hydroxy-DHEAS.
3. This chemical travels to the placenta, where it changes into estriol.
4. Estriol then enters your bloodstream.

When do healthcare providers measure estriol levels?

Providers typically test estriol levels between the 15th and 20th week of pregnancy (during the second trimester). This prenatal test is part of a triple marker or quad marker screening that helps detect congenital conditions (birth defects).

A quad marker screening test measures the hormones estriol and human chorionic gonadotropin (HCG). It also measures alpha-fetoprotein (AFP) and inhibin-A proteins.

Your provider may order an estriol blood test or a quad screen if you have risk factors for congenital conditions, like:

• Being age 35 or older (advanced maternal age)
• Diabetes
• Biological family history of congenital conditions
• Viral infections like hepatitis A or Zika virus during pregnancy

How do healthcare providers measure levels?

A blood test or urinalysis measures estrogen levels, including estriol levels during pregnancy. A blood test is a simple blood draw in your healthcare provider’s office or a lab.

A 24-hour urine test is the most accurate way to measure estriol levels. You collect pee (urine) in a container over 24 hours. Then, you return the filled container to your provider’s office or lab for testing.

At-home test kits can measure estrogen in saliva (spit). But if you’re pregnant, your provider will want to use a more reliable method.

What do abnormal estriol levels mean?

During pregnancy, low levels of estriol may show a problem with the placenta. This result can also signal differences in the fetus, like Down syndrome.

A sudden increase of estriol before the 37th week of pregnancy may mean you’re at risk for premature labor.

People who have low levels of estriol right before childbirth may not go into labor on their own. Healthcare providers will use labor induction methods to kickstart labor.

Your healthcare provider will go over the results with you in detail and explain what they could mean. Don’t hesitate to ask questions. Depending on the results, they may recommend follow-up testing (like an ultrasound) or refer you to a genetic counselor.