Motherhood is the gift that keeps on giving. But some of its gifts may be lethal.
Basic human biology teaches that children share cells from both their genetic contributors. But during pregnancy, however, cells not only pass from mother to embryo through the placenta, but embryonic cells walk the placental pathway back to the mother.
Science writer Nancy Shute describes this as “a silent chemical conversation throughout pregnancy, with bits of genetic material and cells passing not only from mother to child but also from child to mother. Scientists increasingly think these silent signals from the fetus may influence a mother’s risk of cancer, rheumatoid arthritis and other diseases, even decades after she has given birth.”
In 1979, researchers at Stanford University discovered cells containing the male “Y” chromosome circulating in the blood of women after pregnancy. Because these cells were genetically male, they could not have been the women’s own, but most likely came from their babies during pregnancy. More recently, researchers from the National Institutes of Health reported finding male DNA in the autopsied brains of women who had borne sons, sometimes even decades ago.
Experts initially believed that, once the baby was born, any fetal cells transferred to the mother during pregnancy would clear away. But Giovanna Cruz, an epidemiologist at the University of California at Berkeley, discovered that “in a subset of women they actually persist for decades.”
This phenomenon—the harboring of a small number of cells (or DNA) that originated in a different individual—is called microchimerism. You may have cells from a variety of different sources coursing throughout your body: from your mother, from your grandmother, and—if you have ever been pregnant—from your children.
How it happens
In July 2012, researchers from Tufts Medical Center published a study in Biology of Reproduction’s Papers-in-Press indicating they had found cells from the placenta and fetus inside the lungs of late-term pregnant mice. While the team remained uncertain how the fetal cells were able to cross the placenta into the mother, they believed there could be “leaky spots” in the cells that form the barrier between the infant’s blood and the mother’s blood in the placenta in late-term pregnancy.
Dr. Lee Nelson, an autoimmunity researcher and professor of medicine at the University of Washington acknowledged the transference. “That cells cross the placenta is not surprising. After all, the tissue that connects mother and child is not an impenetrable barricade. It is more like a selective border crossing, allowing passage, for instance, of materials needed for the fetus’ development.”
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