As early as the second week of pregnancy, there is a two-way flow of cells and DNA between the fetus and the mother. Cells containing DNA from the fetus cross the placenta and enter the mother’s blood circulation, while cells from the mother cross in the opposite direction and transfer into fetal circulation. Most of the cells coming from the fetus are destroyed by the mom’s immune system, but some persist and become embedded in various organs, and become a part of the parent. This phenomenon is called microchimerism, from the word “chimera,” referring to a mythical creature made from parts of different animals.