If you ask any mother, they will most certainly tell you that having a child had a lasting impact on them. But little did they know becoming a mother may have made more of a difference on them than they imagined. Researchers are finding that during pregnancy cells of the fetus will travel from the placenta to other areas in the mother’s body. Sometimes they will be destroyed once the mother gives birth, but in some cases they can remain in the mother’s body for years after having a child. Whether this will help or hurt the mother is the precise question researchers from Arizona State University are asking.

Microchimerism, or the term used to describe fetal cells migrating to maternal tissue, has been a conflicting topic of research, often reaching contradicting conclusions about just what role these cells play in the mother’s body. Researcher Dr. Amy Boddy of the Department of Psychology at Arizona State University, along with other colleagues have decided to compile all of this research in their most recent study to help evaluate what we know about microchimerism so far.

“These cells have stem-like properties, so they can differentiate into many different tissues,” Boddy told Medical Daily. “There are hundreds of things that they can be doing in the maternal body. If they’re in the blood most of them get cleared, but some stay around. How they stay around we don’t really know … but studies have shown that they do integrate into a tissue, and they grow and proliferate.”

Helpful or hurtful?

For their study, published in the journal Bioessays, Boddy and her team of researchers looked at existing literature on microchimerism to see the possibilities of how it affects the mother’s health, while also looking at this research through an evolutionary lens to see possible adaptive advantages of having fetal cells migrate in this way.

When looking at existing information, researchers have found that fetal tissue is not killed once it leaves the placenta to travel into the mother’s body; in fact, it can persist for decades offering a form of protection, or increasing the vulnerability to different types of cancers and autoimmune diseases like rheumatoid arthritis.

But co-author Melissa Wilson Sayres of the Biodesign’s Center for Evolution and Medicine suggests it’s not that simple. "It's not only a tug of war between maternal and fetal interests," she said. "There is also a mutual desire for the maternal system to survive and provide nutrients and for the fetal system to survive and pass on DNA."

Researchers believe that if fetal microchimerism has some degree of benefit on survival for both the mother and child, then it must be an adapted evolutionary advantage. But, current research isn’t making this conclusion so clear-cut; existing data has suggested that fetal tissue can cooperate with maternal tissue to benefit the mother, invade the mother’s tissue and compete for resources, or simply exist without damaging or benefiting the mother in any way.

For example, in detrimental instances, fetal tissue can trigger the inflammatory response within a mother; seen as foreign invaders by the mother’s immune system, immune cells will attack the fetal cells as if it were a pathogen. Some researchers believe that this is why there are more instances of autoimmune disease in women, than in men.

But there have also been observed instances of fetal tissue repairing damaged tissue within the mother’s body. For example, researchers have observed fetal tissue within caesarian incisions. And then, there are instances where fetal tissue will do nothing. Previous studies have found fetal cells in the mother’s lungs, where they will persist, but not cause any changes to the environment.

The Physiological Effects

When it comes to specific parts of the mother’s body, fetal cells have a very interesting impact on breast tissue. Out of all the women observed within their study, researchers found that fetal cells could be detected in half of participants’ breast tissue. When looking to evolution, researchers hypothesize that 160 million years of co-evolution of maternal and fetal cells may make fetal cells essential to breast development and lactation in a pregnant mother.

Those who believe that fetal cells act intentionally and to benefit the mother, link fetal cell presence with the mother’s ability to lactate. To test this in the future, researchers could look to see whether women who have difficulty lactating have a low fetal cell count relative to those who do not have this difficulty.

Breast cancer, on the other hand, has a more complex relationship to these fetal cells. Some researchers have found that women who have breast cancer also have a low number of fetal cells compared to healthy women. However, other data has concluded that fetal cells may increase the likelihood of developing breast cancer after pregnancy.

The thyroid has also displayed a fascinating relationship with fetal cells. During pregnancy, the thyroid is known to regulate and transfer heat from the mother’s body to the developing fetus. Because of this, some believe that when fetal cells are found in the thyroid, they are manipulating heat regulation so that the fetus can receive more heat to the detriment of the mother. In addition to this, other studies have observed a high number of fetal cells in thyroid-related diseases like Hashimoto’s thyroiditis, Grave’s disease and thyroid cancer.

For The Future

While the maternal cell-fetal cell connection is not so easily parsed, researchers are hopeful that this avenue of study will open up doors in exploring the health of both mother and child. For instance, they believe that fetal cell presence may one day serve to diagnose and predict long-term diseases in the mother. Also, fetal cells may even offer a means for therapeutic treatment to help problems lactating, wound healing, and tumor reduction.

Also, Boddy says that learning more about fetal cells and how the maternal body tolerates these tissues can have implications outside of both mother and child. “Another next step is that if we can understand how humans can tolerate foreign cells in their body, and it can have huge effects for transplantation,” she said.  “Understanding the dynamic of how a mother’s body can and cannot tolerate fetal cells can potentially show us how a recipient can tolerate donor cells.”

Source: Boddy A, Fortunato A, Aktipis A, et al. Fetal microchimerism and maternal health: A review and evolutionary analysis of cooperation and conflict beyond the womb. Bioessays. 2015.