Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Reproductive immunology refers to a field of medicine that studies the phenomenon of immunological tolerance achieved when the mother's immune system accepts the foreign embryo. The concept has also been used by fertility clinics to explain the fertility problems, recurrent miscarriages and pregnancy complications observed when this state of immunological tolerance is not successfully achieved. Immunological therapy is the new up and coming method for treating many cases of previously "unexplained" infertility or recurrent miscarriage.