“…Second, the immunological capacity of the mother may be reduced by certain substances during pregnancy so as to prevent rejection of the fetus (1,5,14,21,22,23,26,37,39,41,49,51,52,55,58). Other evidence, such as the suppressed repsonse to PPD (50), increased isolation of cytomegalovirus (33) and decreased resistance to infectious diseases (18,20,34,46,54) during pregnancy has suggested that the immunological competency of the mother is impaired during pregnancy. However, if the overall level of maternal immunoreactivity during pregnancy is conceded as being lowered, the information is not yet available which allows us to determine whether this is only a result of the pregnancy or it is what enables the fetus to survive in the mother's uterus.…”