09/06/2025
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During pregnancy, fetal cells migrate out of the womb and into a mother’s heart, liver, lung, kidney, brain, and more. They could shape moms’ health for a lifetime, Katherine J. Wu reported in 2024: https://theatln.tc/qozjIdje
The presence of these cells, known as microchimerism, is thought to affect every person who has carried an embryo, even if briefly, and anyone who has ever inhabited a womb. The cross-generational transfers are bidirectional—as fetal cells cross the placenta into maternal tissues, a small number of maternal cells migrate into fetal tissues, where they can persist into adulthood.
Genetic swaps, then, might occur several times throughout a life. Some researchers believe that people may be miniature mosaics of many of their relatives, via chains of pregnancy: their older siblings, perhaps, or their maternal grandmother, or any aunts and uncles their grandmother might have conceived before their mother was born. “It’s like you carry your entire family inside of you,” Francisco Úbeda de Torres, an evolutionary biologist at the Royal Holloway University of London, told Wu.
Some scientists have argued that cells so sparse and inconsistent couldn’t possibly have meaningful effects. Even among microchimerism researchers, hypotheses about what these cells do—if anything at all—remain “highly controversial,” Sing Sing Way, an immunologist and a pediatrician at Cincinnati Children’s Hospital, told Wu. But many experts contend that microchimeric cells aren’t just passive passengers. They are genetically distinct entities. And they might hold sway over many aspects of health: our susceptibility to infectious or autoimmune disease, the success of pregnancies, maybe even behavior.
If these cells turn out to be as important as some scientists believe they are, they might be one of the most underappreciated architects of human life, Wu writes.
