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Immunologic Causes of Recurrent Pregnancy Loss
a blog by Joseph A. Hill, III, MD, Fertility Centers of New England, September 1, 2010
Our immune systems evolved to protect us from non-self, genetically different tissue, also known as allogenic tissue. Immunity can be either innate (inborn) or adaptive (acquired) depending on the molecule that causes an immune response, also known as the antigen.
An immune response involves the production of antibodies (a humoral response) or soluble proteins called cytokines (a cellular response). Potential immune-mediated causes of recurrent pregnancy loss are controversial.
It is important to realize that a successful pregnancy does not depend on a woman having an intact, fully functioning immune system. We know this because both people and laboratory animals incapable of making antibodies (humoral immunity) can have successful pregnancies. Similarly, successful births can also be accomplished in women with severe immune deficiencies and in laboratory animals that lack the capability of making either a humoral or cellular immune response.
The immunologic theory that has been linked to recurrent pregnancy loss is antiphospholipid syndrome, which involves antiphospholipid antibodies, particularly anticardiolipin antibodies. Whether the syndrome is causative, coincidental or a consequence of pregnancy loss remains controversial. How pregnancy loss occurs in cases involving anticardiolipin antibodies is thought to be related to thromobosis or clotting of blood vessels in the placenta.
Antiphospholipid syndrome is not a cause of infertility or early first trimester losses.Pregnancy loss in such cases generally occurs after the first trimester, with the average time of loss being 20 weeks of gestation.
Other immune theories involving cellular immunity have been proposed, but remain less well studied. It has been suggested that the immunosuppressive effects of progesterone within the uterus at the maternal-fetal interface are at least partially responsible for the immunologic acceptance of the genetically different fetus.