Pregnancy has historically been viewed as a conflict between mother and the fetus for survival. This traditional view is based on the fact that as 50% of the genetic information of the fetus is from the father, the maternal immune system sees the pregnancy as foreign and mounts an immune response to reject it. According to this outdated view, miscarriage and implantation failure after IVF result from an excessive immune response by the mother which leads to pregnancy failure.
However, there is NO evidence to support the concept of rejection, which from an evolutionary point of view makes no sense.
Instead, the contemporary view of reproductive immunology is that pregnancy far from being a battle between mother and fetus for survival is a co-operative venture between the two. The latest research indicates that miscarriage is due to a loss of ‘tolerance’ by the mother rather than an excessive immune response leading to rejection.