Babies Never Leave You, or at Least Their Cells Don't

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You might think that once you give birth to a child that they're no longer a part of you physically—except, of course, for the complete control they retain over your heart and mind. Well, think again, because it turns out that during pregnancy some of their cells scatter in your body and stay there for years, maybe even forever. So they are literally a part of you. It's hard to decide whether that is magical or deeply creepy.


While it's been known for a while that fetal cells migrate into a mother's body during pregnancy, it hasn't really been understood what types of cells stick around and what they do. So Diana Bianchi, Executive Director of the Mother Infant Research Institute at Tufts Medical Center, and her colleagues have done a new study on pregnant mice that sheds some light on what exactly is happening during this little alien invasion.

In their study, Bianchi's team found cells from the placenta and the fetus inside of a pregnant mouse's lungs. Eek. They were able to determine that some of the cells were immune cells, while others were undefined connective tissue. Doesn't sound like the most useful thing to have in one's lung, but who can argue with nature? It's not totally clear in the first place how the cells even get across the placenta and into the mother's body, but researchers speculate that the are leaky spots the cells that form the barrier in the placenta that keeps the baby's blood separate from the mom's blood. Regardless of how they get there, they do get there and they make themselves quite at home.

To track the fetal cells, Bianchi's team used a male mouse that had two copies of a green fluorescent protein gene and mated him with a normal female. That meant that the every fertilized fetus carried the fluorescent protein gene, so when its cells made it into the mother, researchers could recognize the fluorescent signal and could distinguish them from the mother's own cells. Once they were able to locate the fetal cells in the mother's lungs, they analyzed the genes that were turned on in any given cell to figure out what function the cell had. They found some were placental cells, and then there were two kinds of fetal cells: immune cells and mesenchymal cells, which are stem cells that develop into connective tissues. What does this mean, exactly? Diana Bianchi explains:

We and other people have shown they stay around for decades. They aren't the original cells so there must be some way they can give rise to daughter cells in the mother's body. We strongly believe that there are implications for the future health of women who are or have previously been pregnant.

That sounds a bit ominous. What kind of implications are we talking here? Like a clone fetus spontaneously forms in your lungs or like the fetal cells do something nifty to pay the mother back for carrying the baby for nine months? Fortunately, it seems to be more on the positive side of the spectrum, though it's not 100 percent clear what the cells do. It's thought that the immune cells function by protecting the fetus from rejection by the mother's body. But researchers believe the mesenchymal cells might help in regenerating or healing tissue inside the mother. Previous research has shown, in fact, that these cells can heal injured maternal heart tissue. Hey, look at that, not only does your child have the power to break your heart, they also have the power to heal it. That's some heavy shit.

Further research needs to be done to figure out exactly how exactly this regeneration works and if there are other roles the fetal stem cells play. How much do you want to bet that they'll eventually discover that it's those crafty little cells that allow kids to exert control over their moms for life. Need a hug? A ride to the mall? Some money? Just activate your sleeper cells and suddenly your mother is physically incapable of resisting you. See? Nature knows what it's doing and is always looking out for you.


Baby's Cells Mix and Mingle with Pregnant Mom's [Live Science]

Image via Tinydevil/Shutterstock.



As an immunologist, I've know this for years. It's called "post-pregnancy chimerism," and previously, studies looked at women who had sons for detection of Y chromosomes. While the number of cells that are from fetal tissue are quite low, they can still be found in women up to 27 years after birth! Woman who also have these detectable fetal cells have higher levels of autoimmune issues like systemic sclerosis.

(If you're more curious, look up Bianchi, 2004, "Fetomaternal cell traffic, pregnancy-associated progenitor cells, and autoimmune disease" in Best Practice & Research Clinical Obstetrics & Gynaecology)

Summation of all this? Just another not so cool thing women get to deal with when they have babies.