some human beings carry remnants of other human beings in their bodies

In addition to the creation of the placenta, the inter-connectedness between the prenatal child and her mother is intimate and more profound than previously believed. We know that genetic material from the prenatal child crosses through the placenta and can be found in her mother’s circulation. This DNA is analyzed in some of the prenatal screening tests done to look for chromosomal abnormalities. The interaction at the level of genetic material however between mother and prenatal child goes much beyond that of a transient crossing of genetic material into maternal circulation. This is illustrated in what is called “microchimerism.”

The “chimera” in Greek Mythology is the fire breathing creature that is made of three distinct creatures—a lion’s head, a goat’s body and a serpent’s tail. In science, microchimerism is the presence of a small population of genetically distinct and separately derived cells within an individual. The growing baby sends some of her cells across the placenta into her mother in a way that we are only beginning to understand. These cells migrate to various sites of maternal tissue and integrate into them. They then assume the function of the surrounding tissue and begin to function as such. The presence of fetal cells in maternal tissue is known as fetomaternal microchimerism. 

Microchimeric cells have been found in various maternal tissues and organs, such as the breast, bone marrow, skin, liver and brain. Early and late effects of these cells have been hypothesized. Some of these cells appear to target sites of injury and may help mother heal after delivery by integrating into the Cesarean section wound and helping to produce collagen. Fetal cells may be involved in the process of lactation by signaling the mother’s body to make milk. Others have been thought to help protect a mother against breast cancer later in life. This process likely involves negotiation and cooperation between mom and baby at the cellular level. Researchers are in the early stages of attempting to understand the full function of these cells, but some models suggest that some of these cells continue to aid the mother years after her baby is born and may even influence spacing of future siblings. There is increasing evidence that fetomaternal microchimerism persists lifelong in many childbearing womenand may have important implications for the immune status of women. Some studies suggest that fetal cells protect women against autoimmune disorders. The full significance of fetomaternal microchimerism remains unclear and in some studies the cells have been linked to higher rates of diseases. The reality of this process challenges our long standing ideas about human beings existing as singular autonomous individuals.
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