Scientists have long had to grapple with the fact that it is less surprising that some pregnant women reject their fetuses than that any fetus, in fact, makes it through to full-term birth. Why? Because the process of conception, fertilization, and embryological development go against one of the basic tenets of nature: the body, as transplant surgeons well know, rejects anything it dose not recognize as its own. The embryo is only 50percent its mother’s tissue; the other half, which comes from the father, is considered by her body to be foreign tissue.
In the very early days following conception, the trophoblast, the bundle of fetal cells of the developing embryo and placenta, actually comes in contact with the mother’s tissue and her blood as it attaches to the uterine wall. The mother’s blood cells make antibodies to this partly “foreign” tissue, as would be expected.
Normally, however, a pregnant woman will also make from the antibodies that protect these trophoblast cells from the antibodies formed. These special antibodies, peculiar to the pregnant state, are known as blocking antibodies.
The precedent to this type of research was found in the world of kidney transplants. Doctors, struggling to find ways to encourage their patient to accept a donor kidney, found their tolerance was increased if they had previously had a blood transfusion.
A woman who becomes pregnant has naturally been exposed to her partner’s foreign cells through intercourse. Semen carries some tissue proteins, called antigens (that is, proteins that trigger an antibody response). It doesn’t matter how many times you have had intercourse previously; even once is enough.
Doctors used to think that in pregnancy the immune system was suppressed. In fact, in a curious reversal of normal situations, it is the underactive immune system not recognizing this tissue as foreign that prevents the “blocking antibody” from being made, not, as you might imagine, a widely aggressive immune system attacking all foreign tissue at will. It is now believed that certain men and women are genetically too similar (though if your husband had to donate his kidney to you, the similarity would have its advantages). In this case, the woman adopts the husband’s antigens as her own.
There is no way of knowing beforehand who will be affected, though is does lend credibility to the Biblical juncture against marrying a first cousin or a very close relative. The problem is “asyptomatic,” meaning you have no symptoms such as high temperature or nausea. And how much you love your partner bears not the slightest relevance. From studies, it has been found that there is a percent chance, in a randomly selected sample of couples, that you will share major antigens.
In the mid seventies, researchers began to detect the “blocking factor” in pregnant women. Research on this subject was begun both in Britain and the United States. Dr. Mowbray at saint Mary’s Hospital, in London, began testing women, and then immunizing them with their own white blood cells or with their partner’s. At least twice as many women who had previously miscarried more than three times went on to have full term babies if they had been injected with their partner’s white blood cells. With this technique the success rates vary, but there is at least a 75 percent success rate for women who have had between three and six previous miscarriage. Women with successful pregnancies were studied, and one could see that, by comparison, women who were miscarrying lacked a certain substance called blocking factor that could be detected in the blood. White cell immunization treatment may increase amount of blocking antibody or stimulate protective immune suppressor cells in order to help the pregnancy survive.
