Faith & Science
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By Amanda Alexander

As I write this article, I am less than a week away from delivering my second child. Thanks to a simple blood test, I’ve known since I was about fourteen weeks pregnant that I am expecting a boy. The blood test is routinely offered to pregnant women to screen for any genetic concerns. It’s non-invasive, and I opted to have it done so that I could be as prepared as possible to meet the needs of my child. The test is able to detect the sex of the fetus, amongst other things, because, beginning very early in pregnancy, fetal cells cross the placental barrier and actually circulate in the bloodstream of the mother. The phenomenon is known as microchimerism.

Despite the report from the blood test, I wasn’t entirely convinced I was having a boy until I saw the evidence for myself on the ultrasound scans conducted when I was twenty weeks pregnant. I was skeptical because, about six months before I conceived this child, I had a miscarriage. According to what I was able to learn from internet searches about microchimerism, the miscarriage occurred after fetal cells would have begun to circulate in my blood. What surprised me was how long those stem cells could remain in my body: for the rest of my life. Even though two months after a pregnancy ends fetal cells are no longer detectable in the mother’s blood, they have been detected in the mother’s organs decades later.

Our scientific understanding of microchimerism is still developing, but we know that there are at least three different types of microchimerism. Fetal microchimerism refers to the presence of fetal DNA in the mother; maternal microchimerism describes the phenomenon of maternal cells found in the woman’s children (thought to occur as a result of breastfeeding); and third type of microchimerism results from the transfer of DNA material between twins while they are still in the womb. A recent study even found evidence of a fourth type of microchimerism called grandmaternal microchimerism in which genetic material from a grandmother was found in fetal cord blood.

Scientists who study these different types of microchimerism seek to understand not just how the genetic material is transferred, but also the long-term effects of the presence of one person’s genetic material in another individual. Some studies of fetal microchimerism suggest that the continued presence of fetal cells in the mother after a pregnancy has ended may explain the higher prevalence of autoimmune diseases in women. However, other studies suggest that these fetal cells may act as stem cells in the mother’s body and actually help to repair damage caused by disease. The presence of maternal cells in female children is thought to give them a reproductive advantage.

My own reflection on the possibility that a child’s cells could remain in a mother’s body for the rest of the mother’s life has, as you probably suspect, taken me down a number of different paths. At a profoundly personal level, there is a great sense of comfort and joy in knowing that, regardless of the outcomes of my pregnancies, I may carry some part of my children with me always.

At a more speculative level, I have found myself wondering how microchimerism might shed light on our Catholic belief that Mary was assumed bodily into Heaven. It is very possible that cells from Jesus’ body remained in Mary’s body even after she gave birth. The connection between mother and Son at the point of what would have been her death would not just have been spiritual, but also truly physical. Perhaps what happened at that moment was triggered by those cells, and that physical connection is what gave Mary such a unique relationship to her resurrected Son’s body that her own body was assumed into Heaven.

These thoughts are, of course, speculative and in no way meant as an apologetic defense, let alone a definitive explanation of one of the great mysteries of our faith. While I appreciate the potential of microchimerism to explain the mystery of the Assumption, what resounds in my heart is instead a promise: “Behold, I am with you always, until the end of the age” (Matthew 28:20).

Amanda Alexander is currently the Director of the Department of Ministry Formation Institute for the Diocese and a parishioner of St. Adelaide in Highland. She has a Ph.D. in systematic theology and has taught at numerous Catholic universities.