Your baby might inherit your blue eyes or your narrow feet. But did you know your baby in the womb could pass on something to you that might impact your health decades later?
When you’re pregnant, cells from your baby can cross the placenta and circulate in your blood and take up residence in your organs, just as your cells can cross the placenta and enter your baby’s circulation.
You’ve probably heard about the prenatal screening tests that pull fetal DNA fragments out of the mother’s blood and analyze them for chromosomal disorders such as Down syndrome. Those fragments, remnants of whole fetal cells, vanish after only a few hours. But intact fetal cells can travel in the mother’s blood and hang around for decades after she delivers her baby. Same goes for her cells in her children.
The presence of fetal cells in the mother or maternal cells in her child is called “microchimerism,” a reference to chimeras, strange hybrid beasts in Greek mythology, such as the part man, part horse centaurs. Cells begin crossing the placenta early in pregnancy, and their numbers increase as time passes, peaking at delivery. By that point, according to one estimate, fetal microchimerism occurs in about half of pregnancies, while maternal microchimerism is a little less common.
Those escaped fetal cells appear to play a bigger role than other pregnancy souvenirs, such as stretch marks. In a new article on the subject, Arizona State University researchers write that they “can perhaps be considered a far-reaching extension of the placenta.”
The ASU scientists speculate that fetal cells in the mother can increase milk production and quality, raise her body temperature to help keep her baby warm and enhance attachment and bonding with the baby. After the child is grown, though, fetal cells in the mother might make her more susceptible to autoimmune diseases and developing cancer.
However, a Danish study of 272 women published in 2014 found that that the 70% who had male cells in their circulation lived longer overall than those who didn’t.
(Don’t think you’re at a disadvantage if you’re carrying a girl. The scientists say they focused on male fetal cells circulating in women because, not surprisingly, they’re easier to pick out in a woman, not because there’s any known survival advantage to conceiving a son instead of a daughter.)
The women were 50-64 when they joined the study in 1993-1997, and researchers followed them until the end of 2008. During that time, the women with male microchimerism were about 60% less likely than the women without it to have died from any cause. However, the risk of dying differed for different causes of death. Women with microchimerism were about 75% less likely to have died of cancer, but they were about two-thirds more likely to have died of cardiovascular disease.
Their finding about cancer fit with an earlier study by one of the authors that found that the women with male cells in their circulation were more likely to survive a diagnosis of breast or colon cancer. However, the researchers had also reported that women with male microchimerism were more likely to be diagnosed with colon cancer, although less likely to be diagnosed with breast cancer, than women who didn’t have microchimerism.
There are other sources of male microchimerism in women besides conceiving a boy, such as receiving a blood transfusion from a male donor or having a twin or older brother, the researchers note. (The older brother’s cells would have been passed to his mother when he was in the womb, and then, in her subsequent pregnancies, she could pass those cells to her younger children.)
However, the participants in their study were healthy when they enrolled, making it unlikely they’d had a blood transfusion. The scientists didn’t know whether any of the women had a twin, but, they note, Denmark has a really low rate of twin births.
None of the research so far proves that fetal cells protect against or enhance the risk of any diseases in women. But, as the ASU scientists write, the cells might eventually be useful in diagnosing existing health problems in mothers and predicting their long-term health. And perhaps someday, the researchers say, the fetal cells could be used to help treat cancer, poor milk production in nursing mothers and maybe even psychological disorders linked to pregnancy.