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What Is the Difference between Estriol and Estradiol?

By S. Reynolds
Updated: Mar 03, 2024

Estriol and estradiol, also spelled "oestriol" and "oestradiol," are two types of sex hormones produced mainly by women. Estriol is is the pregnancy hormone and is only found in large amounts during pregnancy, whereas estradiol is found in all women. A developing fetus and placenta produces the estriol hormone naturally.

If a woman wants to know if she is pregnant, a home pregnancy test will look for the appropriate levels of estriol to see if there is a growing fetus. The estriol is present in the blood and also excreted in the urine, so a simple urine test or blood test can show whether or not a woman is pregnant. During pregnancy, a woman's doctor will occasionally check her levels of estriol to see if the pregnancy is progressing normally.

Estriol and estradiol also come in synthetic versions if a woman needs hormone replacement therapy. They are commonly referred to as estrogens. Although women make these hormones in abundance, men also have these hormones in small amounts.

Women who are between the ages of 12 and 40 have the highest levels of estriol. The estrogen levels skyrocket during pregnancy and then taper off during menopause. If a woman is having difficulty with menopausal symptoms, there are hormone supplements she can take.

Estradiol is also a sex hormone that is found in premenopausal women. It is vitally important for sexual and reproductive health, but it also affects other bodily organs, such as the skeletal system. It is very similar to estriol, but has a few differences.

Estradiol is found in large quantities in young women who can still bear children. Estriol, on the other hand, comes mainly from the fetus during a pregnancy. Therefore, post-menopausal women and non-pregnant young women have similar levels of estriol.

A person can find estradiol throughout the entire body, as it is produced in the brain and arteries. Even fat cells create estradiol before and after menopause in women. Men who are obese tend to produce too much estradiol, which can cause bodily feminization.

Women who are going through menopause commonly use estriol and estradiol as part of a hormone therapy or hormone replacement treatment to relieve symptoms such as incontinence and vaginal dryness. The hormones comes in cream form and pill form for convenience. Synthetic estrogens typically are available through pharmacies, but in most countries, one needs a doctor's prescription.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By Slashenden — On Feb 12, 2014
Bio identical hormone therapy is being chosen by more women over traditional hormone replacement therapy. This came about several years ago when the medical community linked these hormones to breast and other cancers, causing some women to elect for no hormone replacement therapy at all. Dealing with menopause without HRT is difficult at best. The symptoms of menopause (hot flashes, vaginal dryness, lack of sex drive) can be lessened with hormones tailored to the woman and prescribed by a doctor. Bio identical HRT is worth looking into as an alternative to traditional HRT.
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