A proposed mechanism which may explain why the fetus is not considered to be foreign tissue by the maternal system during pregnancy.

A review of laboratory and clinical data is presented which supports a proposed endemic control mechanism designed to destroy the initiation of any localized abnormal growth of cells regardless of whether the cells are normal or aberrant. The emphasis of this article hypothesizes how the endemic control mechanism distinguishes between a fertilized ovum and fetus--which are also foreign to the mother's system--so that the fetus is not rejected by the endemic control mechanism that destroys other types of localized abnormal cell growth in the body. These data support a commonality between endemic control of pregnancy, tissue repair, and cancer growth and development.