Pregnancy and Immune System

Gynecologist and immunologist have been trying to understand the immunological aspect of pregnancy. This is because of the need of finding a good explanation to why an embryo/fetus, considered an allograft, should develop in a woman’s uterus without eliciting an immune reaction followed by rejection of the fetus. There are various theories and questions asked in the course of finding an explanation to this phenomenon. Some of the questions wondered if the uterus was not immunological equipped or an embryo lacks antigens to elicit a reaction. But experiments and other findings disapproved the question. The discovery of placenta confirmed the question on a possible barrier between a mother and a developing embryo. Yet, there are still questions on the immunological aspect of pregnancy especially as immunologist find it difficult to accept.


The importance of the placenta as a biological barrier is established. It serves as a shield that protects the fetus in a foreign environment. It is also known that some substances can pass through the placental barrier and some of them may be harmful to the developing fetus. This is also the case when some infectious agents or harmful chemicals cross the placental barrier. Another important aspect is the hemolytic disease of new born which occurs after a Rhesus factor in the blood of a fetus has sensitized a mother in her previous pregnancy. This may suggest that the immune system of a mother is not aware of all the antigenic component of a fetus because of the placental barrier that shields a fetus in an uterine environment.

Some immunologists view an embryo/fetus as a parasite while others consider it as an allograft. Let us assume that a fetus is a parasite then it follows that an embryo wants to survive just like any other parasite that has mechanisms of invading the human/animal immune system. Consequently, an embryo developed its own ways of invading her mother’s immune system and abortion may result, which is a form of rejection, if a mother’s immune system reacts against the developing young. One of such mechanism is the ability of an embryo to sends signal to announce his or her presence in an uterine environment, followed by alterations in the endocrine pattern of the mother for instance the inhibition of productions of some hormones like PG2 alpha. The “early pregnancy factor” used for early pregnancy diagnosis is said to suppress a mother’s immune system. The fetal hypothalamic-pituitary-adrenal axis plays an important role in termination of pregnancy as an abnormality to the system can result in prolonged pregnancy.

It is said that some abortion occur because of malformed fetuses.

Then if that is the case, if can be said that such fetus fail to produce a mechanism that is necessary for their protection because of such malformation or a mother’s immune system fail to obey the natural events necessary for pregnancy to be carried.


Whatever may be the mystery behind this natural event we know that it is necessary for every species to reproduce its kind. Thereby continue in its existence/survival.




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