A fetus's cells can and do migrate to its mother. Cells pass between a mother and a fetus during pregnancy, after which they can stay in the body and reproduce for decades, a condition called microchimerism. Researchers have found male cells in women's blood after pregnancy, and the cells are also often found in a mother's brain. A mother can also pass cells to a fetus, but this happens about half as frequently as the reverse.
More about microchimerism:
- It's not entirely clear why microchimerism happens, and it's still being researched, but it seems like it may have several impacts on health. Some studies shows that microchimerism may lower a woman's chances of cancer, while others show that it may increase her chances of having an autoimmune disease.
- Some women have male cells in their blood even if they haven't had sons. Researchers aren't sure why this is, but they think that it could be caused by a missed early miscarriage or by the woman's mother passing on cells from the woman's older brother that the mother acquired during pregnancy.
- Microchimerism can also occur in people who get blood transfusions, though it's much rarer than that from pregnancy.