Mothers and their children exchange living cells that survive in each other's bodies for decades, creating a lifelong biological connection.

This phenomenon is called microchimerism — when cells from one individual live within another's body. During pregnancy, the placenta allows bidirectional cell flow between mother and fetus. A 2012 study published in PLOS ONE found male DNA in the brains of 63% of women tested, including some over 90 years old, showing that fetal cells can persist in a mother's body for her entire lifetime.These fetal cells are far more than passive hitchhikers. Research from institutions like the Fred Hutchinson Cancer Research Center reveals that they actively migrate to injury sites, where they differentiate into specialized cells such as heart muscle or neurons to aid tissue repair. This suggests the child's cells may actively support the mother's health throughout her life.Maternal cells also enter fetal circulation and can remain in the child's body into adulthood. This two-way exchange may support immune system development by helping the fetus recognize and tolerate foreign antigens. While microchimerism is generally beneficial, scientists continue investigating potential links to autoimmune diseases and cancer. This cellular exchange has fundamentally reshaped our understanding of biological individuality and the maternal-fetal bond.