During pregnancy, a small number of the baby's cells naturally pass through the placenta and enter the mother's blood circulation. This phenomenon, called fetal microchimerism, allows tiny groups of these fetal cells to settle in the mother's body and persist there for decades following childbirth. What makes this particularly fascinating is that many of these fetal cells function similarly to stem cells. They can travel throughout the body, integrate into various tissues, and, in certain instances, respond to sites of injury. Studies conducted over the last twenty years have detected fetal cells in areas undergoing repair, such as healing heart muscle, regenerating skin, recovering liver tissue, and other organs involved in regeneration. Some of these cells seem able to differentiate into the specific cell types required for repair, for example, becoming cardiac muscle cells, liver cells, or immune cells. Others may play a supportive role by secreting substances that promote tissue healing and dampen inflammation. While their effects are not entirely predictable, fetal cells are repeatedly found in tissues actively engaged in repair. [Kara et al. (2012): "Fetal Cells Traffic to Injured Maternal Myocardium and Undergo Cardiac Differentiation" (Circulation Research)] [Wang et al. (2004): "Fetal cells in mother rats contribute to the remodeling of liver and kidney after injury" (Biochemical and Biophysical Research Communications)]