Reproductive immunology is the field of medicine, that deals with interactions between the immune system and the reproductive system. It involves the immune response of mother to pregnancy, helping in maintenance of healthy pregnancy. Any disturbances in this immune interaction can lead to complications in pregnancy, like pregnancy loss (miscarriage), pregnancy induced hypertension (PIH) or growth restriction of fetus (IUGR).
The immune system
The immune system is our body's protection against any invader. It defends the body against a wide range of pathogens including bacteria, viruses, other micro-organisms and to altered cells of our own body. It is a network of cells, tissues and organs that work together to defend the body against attacks by foreign invaders. Understanding how the maternal immune system responds to pregnancy is critical for our ability to better diagnose, understand and treat various pregnancy complications. This response of immune system to pregnancy is known as alloimmune response.
There is a balance between the activation and tolerance induced by the immune system. This immunological equilibrium is important for protection against autoimmune and alloimmune responses. Any disturbance in this equilibrium will lead to autoimmune or alloimmune disorders.
Fetus is a Semi-allograft
The fetus is 50% from the mother and 50% from the father. So, the fetus is 50% different immunologically from the mother. Hence, fetus is also known as “semi-allograft. In spite of this, the pregnancy continues to grow in the mother’s body without any rejection, as should have happened logically. This is known as “Paradox of pregnancy”. This is possible due to the complex immunological interactions happening at the feto-maternal interface.
Thus, Reproductive Immunology plays an important role in Implantation of embryo, continuation of early pregnancy and subsequent growth of pregnancy. Disturbances in Reproductive immunological mechanisms play a critical part in the causation of fertility related problems like repeated pregnancy loss, recurrent implantation failures and unexplained infertility. In fact, during the last 25 years, it has become clear that a large percentage of the unexplained repeated pregnancy loss/ recurrent implantation failures may be due to alloimmune cause. It has also been seen that more the number of miscarriages, more is the chance of alloimmune factor