Maternal immunologic changes during pregnancy: a critical appraisal.

A great variety of approaches have been applied to the study of immunity during pregnancy. Many of the studies have been motivated by an attempt to explain the failure of of the mother to reject the fetus. At times, dramatic findings have been claimed; and, at times, these results have been held to be expected, since no immunologic event (or nonevent) has been more perplexing than the failure of the mother to reject the fetal "allograft." This review will present clinical findings relevant to an understanding of immunocompetence and host defense during pregnancy, as well as the results of laboratory investigations regarding the possibility of altered immunity during pregnancy.