Embryo Toxic Factor

Because a miscarriage is so common, it is unlikely that any type of medical investigation as to why the miscarriage occurred will be done. Generally, the cause of the miscarriage is associated with some type of genetic problem with the embryo; often a blighted ovum or a molar pregnancy can be blamed.

However, if you have experienced two or more consecutive miscarriages, your health care provider will likely want to take a closer look at the situation. As part of your assessment, it is likely that you will be investigated for embryo toxic factor.

What is It?

Embryo toxic factor (ETF) refers to an immune system response by your body to an embryo. ETF is secreted by your white blood cells. If your white blood cells produce too much ETF, your body’s immune system is likely to recognize an embryo as a foreign invader.

Since the purpose of your white blood cells is to keep your body healthy, your immune system will attack the embryo, causing a miscarriage.


Women who have experienced recurrent miscarriage will be tested for ETF in order to assess whether their body is producing an immune system response to a potential pregnancy.

Testing for ETF is actually a two-part procedure. The first determines whether your cells (or lymphocytes) are producing any type of substance that may be toxic to an embryo. The second stage of the test involves an embryo culture.

During the first part of the test, a sample of your blood will be taken and certain lymphocytes will be isolated. The lymphocytes will then be treated with a special solution and left to culture for several days. After this time, the lymphocytes will be used in an embryo culture.

The embryo culture utilizes two-cell stage mouse embryos to determine whether the lymphocytes are secreting any type of toxic substance. The lymphocytes are left to culture with the mouse embryos for a few days before fertility specialists return to examine how well the mouse embryos have developed.

Embryos that have stopped developing or died indicate the presence of ETF. If normal cell division has occurred, then it can be concluded that no ETF is secreted by the lymphocytes.


Women who have tested positive for ETF will require treatment that suppresses their immune system. By suppressing the immune system, an embryo will be able to implant and develop normally without any interference from your body.

Typically, treatment involves using vaginal progesterone suppositories twice a day from the time of fertilization up to the 16th week. Dosage can vary from woman to woman, but usually ranges between 200mg and 400mg.

Although progesterone is more commonly used for increasing hormonal levels, thereby helping regulate the menstrual cycle as well as strengthening the uterus, in high doses it can also have an immunosuppressive effect.

If you continue to experience multiple miscarriages, the dosage of progesterone may be increased. Alternately, it may be possible to receive IVIg infusions as IVIg helps to suppress the immune system as well.


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