Estriol, what it is and how it works

Estriol is a natural estrogen whose concentration rises significantly during pregnancy. It is also present in some preparations for hormonal therapies.

Estriol, also called E3, is one of the three sex hormones (estrogens) produced by the female body. The other two estrogens are estradiol and estrone.

The sex hormone estriol

Estriol, also called E3, is one of the three sex hormones ( estrogens ) produced by the female body . The other two estrogens are estradiol  and estrone .

Estriol is an androgen hormone, i.e. a hormone produced by the adrenal and sexual glands. During  pregnancy , its concentration in the body rises significantly.

It is mainly produced by the ovaries but, during pregnancy, it is also produced by the placenta: it is produced by the placenta from an androgenic steroid (DHEAS 16-OH) which in turn is produced by the fetal liver and adrenal glands.

The activity of estriol in the body

Hormones  are chemical substances that act as messengers, in the sense that they transmit signals from one cell/several cells to another/e, and in this way serve to control and coordinate the way our body functions and responds.

During a pregnancy, women produce many hormones, this because their presence in their body is useful not only for their health (the mother), but also for that of the fetus.

The amount of one of these hormones, estriol , peaks just before the baby is born.

Estriol is also an indicator of fetal health because the chemical from which it is produced (in the placenta) comes from another chemical which is first produced in the baby’s adrenal glands, then altered in the fetal liver before eventually be converted to estriol in the placenta.

Estriol causes uterine growth and increases its sensitivity to other pregnancy-related hormones, thus gradually preparing the woman for childbirth.

Estriol levels begin to rise from the eighth week of pregnancy : some argue that labor begins when estriol becomes the dominant hormone.

How it is produced in the female body

As we have said, estriol is produced by the placenta from a chemical substance that comes from the fetus:

  1. The fetal adrenal glands first produce a hormone called dehydroepiandrosterone sulfate (DHEAS).
  2. DHEAS is then transported to the fetal liver and transformed into 16a-hydroxy-DHEAS.
  3. The 16a-hydroxy-DHEAS is – in turn – transported to the placenta where it is transformed into estriol.

Most of the time of pregnancy, the greatest amount of estriol produced by the placenta is bound to other chemical substances which inhibit it from producing biological effects.

Estriol levels too low

In non-pregnant women , estriol is found only in very low amounts.

During most of the time period of pregnancy, the major amount of estriol produced by the placenta is found bound to other chemicals that inhibit it from producing biological effects.

In pregnant women , too little free (unbound) estriol can indicate problems with the baby, such as  Down syndrome  or complications with the placenta such as placental abruption (premature detachment from the uterine wall ) or as a placenta previa (implanted near the cervix, in the lower part of the uterus).

Later in the pregnancy , a relatively low estriol level indicates that labor may not come on its own, but  will need to be induced .

The sudden increases in its levels

About three weeks before labor, there is a sudden rise in estriol. If the increase were to come too soon, this fact may suggest that you could face a premature birth.

The therapeutic uses of estriol

For hormone replacement therapies . Currently there are medicines based on the active ingredient estriol which are subject to medical prescription with RR Recipe.

Estriol is mainly used in the so-called hormone replacement therapy (HRT), a pharmacological treatment based on hormones aimed at compensating the lack of female hormones (estrogens) typical of menopause or following the surgical export of the ovaries.

In Italy, among the drugs based on estriol, we recall those marketed under the names of OVESTIN ® and Colpogyn. But there are others too.

Its other possible therapeutic uses.  It has been observed in some women with autoimmune diseases that their symptoms improve during pregnancy but especially in the later stages of pregnancy when their estriol levels are higher.

Based on these observations, some researchers are trying to understand if estriol is also able to suppress our immune system. If so, it could be used to relieve some of the symptoms of certain medical conditions such as multiple sclerosis and rheumatoid arthritis.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

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