Lisa Merry

Read the first page below or click here to read the entire essay: Lisa Merry – Why Doesn’t a Pregnant Woman Reject her Fetus

Recurrent Pregnancy loss (RPL) occurs when a woman has three or more consecutive miscarriages; this phenomenon happens in about 1-3% of women. Why some women reject their unborn fetus and others carry theirs to term is still unclear. There are four main theories that exist regarding why some women reject their fetus and others do not: the maternal immune system might not be capable of responding to fetal antigens due to mechanisms that induce tolerance in responding maternal cells; a “barrier” may from between mother and fetus, preventing access of maternal immune cell to fetal antigens; fetal cells may suppress the expression of their antigens; and the fetus may generate site-specific immune suppression. We will look closely at two studies that ask the questions: does the non-specific immune response increase to compensate for the decrease in specific immunity? Is there a maternal cell-mediated immune response to the fetus which needs to be blocked, and do blocking antibodies develop in all successful pregnancies? Different aspects of each theory have proven that a maternal cell-mediated response is not acquired at any stage in pregnancy to the fetus but monocyte surface expression is increased. This proves that there is an increase in the innate immune response. Future studies will look more strictly at the differences between these main theories.

Background

Pregnancy has become a lot safer than in the past due to technology in medicine and a higher level of education for our health care professionals. Still little is known as to why pregnancies for some women are successful and for other women they are not. 50-60% of pregnancies have a common complication called spontaneous miscarriage, defined as the spontaneous end of a pregnancy that occurs prior to 20 weeks gestation where the embryo or fetus is incapable of surviving; a less common form of miscarriage is recurrent pregnancy loss, or RPL, which occurs in 1-3% of women and is defined as three or more consecutive miscarriages prior to 20 weeks gestation (Saini V., et al. 2011).

There are four different theories experts have studied to understand why this occurs. First, due to mechanisms that induce anergy, reduction or lack of an immune response to a specific antigen, the maternal immune system might not be capable of responding to fetal antigens (Koch and Platt 2007). Second, an anatomical barrier may form that prevents access of maternal immune cell to fetal antigens between mother and fetus (Koch and Platt 2007). Third, fetal cells may suppress the manifestation of alloantigens; an alloantigen is any antigen, present in only some individuals of a species, which stimulates the production of antibodies in those that lack it (Koch and Platt 2007). Finally, the fetus may create site-specific immune suppression in which maternal immune cells would then be blocked, defending the fetus while permitting the cells to produce an immune response (Koch and Platt 2007).

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