Microchimerism: Defining and redefining the prepregnancy context – A review

Bidirectional transplacental exchange characterizes human pregnancy. Cells exchanged between mother and fetus can durably persist as microchimerism and may have both short- and long-term consequences for the recipient. The amount, type, and persistence of microchimerism are influenced by obstetric characteristics, pregnancy complications, exposures to infection, and other factors. A reproductive-aged woman enters pregnancy harboring previously acquired microchimeric “grafts,” which may influence her preconception health and her subsequent pregnancy outcomes. Many questions remain to be answered about microchimerism with broad-ranging implications. This review will summarize key aspects of this field of research and propose important questions to be addressed moving forward. •Bidirectional transplacental exchange during pregnancy can result in cellular microchimerism.•Microchimeric grafts and their interactions may impact host health and reproductive outcomes.•Infectious diseases may provide insight into evolutionary pressures on microchimerism.