Having a baby changes you in more ways than you might imagine. Aside from the stubbornly thicker waist, saggier boobs, and the crash course in multi-tasking (simultaneously mopping up vomit, breastfeeding a newborn, and pressing play on a Disney DVD to occupy your neglected toddler, for example), you will forever carry little pieces of your children around inside of you–literally.
From early pregnancy, cells from your developing baby make their way across the placenta into your bloodstream, ultimately setting up camp in your bone marrow. This may sound sinister: Babies already sap your energy; now they’re sucking on your bones?! But this process may come with benefits for mom, as it increasingly looks like these fetal cells could help to protect us against future diseases, including cancer. You can look at it as a kind of fetal insurance policy that boosts the chances of mom surviving long enough to support her offspring into adulthood.
This encroachment of baby into mom starts from around four to six weeks of pregnancy, before many women even realize they’re pregnant, and continues until the baby’s birth. Even though these cells are essentially “foreign” and should therefore trigger an immune reaction in the mother, they don’t seem to in most women—although some scientists have suggested that as well as protecting mom against disease, fetal cells may occasionally contribute to auto-immune diseases such as rheumatoid arthritis or lupus.
Cells containing fetal DNA have been recovered from the livers of women with hepatitis C, suggesting that these cells may have lodged there and transformed into liver cells to help patch up the damage caused by the disease. Meanwhile, women with breast and other cancers seem to have fewer fetal cells in their blood than healthy women, hinting that this fetal repair kit may help protect women against the disease—possibly by helping the immune system to identify and destroy cancer cells before they take hold.
Moms often talk about having baby brain, but it’s quite possible your mind becomes a haven for baby’s cells as well. Animal studies have suggested that fetal cells can travel into the brain, where they mature into different cell types, including neurons (which transmit electrical signals throughout the brain) and the cells that nurture and support them.
The whole concept is dubbed “fetal microchimerism,” and what it means is that the more children you have, the more of a mosaic of different people your body becomes. You are no longer just you; you are you plus your children–possibly long after they have grown up and flown the nest.
It works in reverse, too. Babies get a transfusion of their mother’s cells during pregnancy, and these can also stick around for years. There’s even evidence that these maternal cells may help baby girls to have a successful pregnancy of their own once they grow up. Preeclampsia is a serious complication of pregnancy affecting 6 to 8 percent of women and is characterized by high blood pressure and protein in the urine. Its exact cause is unknown, but one theory is that it is triggered by the mother’s immune system over-responding to the pregnancy.
When Hilary Gammill at the Fred Hutchinson Cancer Research Center in Seattle investigated how a woman’s risk of preeclampsia related to the number of maternal cells she harbored, Gammill found that the number of these maternal cells usually increased as pregnancy progressed, suggesting that an existing population of maternal cells was being either expanded or mobilized from somewhere in the body.
But whereas around 30 percent of healthy women had detectable levels of maternal cells in their blood by the third trimester, no such cells could be found in the women with preeclampsia, hinting that the maternal cells may be having some kind of protective effect. One possibility is that they may help train a woman’s immune system to be more tolerant of cells from the fetus.
In other words, Grandma may be indirectly helping to safeguard the survival of her family long after her own body has ceased to bear children.
Personally, I’m stockpiling this knowledge for when my (currently young) daughter turns into a snarky teenager. My retort to the inevitable declaration of “Mom, I hate you!” will be something to the tune of, “Yeah? Well, I’m inside you and I always WILL be. Freaky, huh?!” That’s the trouble with families: They’re pretty much inescapable.