Fetal cells play a role in maternal health

Here are some fascinating excerpts from Do Chocolate Lovers Have Sweeter Babies? - a new book about the biology of pregnancy:

During pregnancy, cells sneak across the placenta in both directions. The fetus’s cells enter his mother, and the mother’s cells enter the fetus. A baby’s cells are detectable in his mother’s bloodstream as early as four weeks after conception, and a mother’s cells are detectable in her fetus by week 13. In the first trimester, one out of every fifty thousand cells in her body are from her baby-to-be (this is how some noninvasive prenatal tests check for genetic disorders). In the second and third trimesters, the count is up to one out of every thousand maternal cells. At the end of the pregnancy, up to 6 percent of the DNA in a pregnant woman’s blood plasma comes from the fetus. After birth, the mother’s fetal cell count plummets, but some stick around for the long haul. Those lingerers create their own lineages. Imagine colonies in the motherland.

Moms usually tolerate the invasion. This is why skin, organ, and bone marrow transplants between mother and child have a much higher success rate than between father and child...

It turns out that when fetal cells are good, they are very, very good. They may protect mothers from some forms of cancer. Fetal cells show up significantly more often in the breast tissue of women who don’t have breast cancer than in women who do (43 versus 14 percent)... There’s also tantalizing evidence that fetal cells may offer the mother increased resistance to certain diseases, thanks to the presence of the father’s immune system genes...

Fetal stem cells migrate to injury sites... they accelerate healing, reducing scars after pregnancy and restoring the normal structure of the skin...

Researchers working with mice have found evidence that cells from the fetus can cross a mother’s brain-blood barrier and generate new neurons. If this happens in humans—and there’s reason to believe it does—then it means, in a very real sense, that our babies integrate themselves into the circuitry of our minds...

Fetal cells may be harvested from the blood or organs of mothers and potentially be used as a source of cells with regenerative properties for a mother and her children. They have advantages over other stem cells in that they don’t require the destruction of embryos or require cell cultures and potential contamination. They’re unlikely to be rejected by the mother or child because, from an immune-system perspective, they’re only part “other.” 

The downside is that fetal cells in the mother can also serve as stem cells for cancer, and may trigger "autoimmune" disorders.  There's a brief discussion of this at the link (via BoingBoing), and obviously more in the book.