Microchimerism: A complex memento of pregnancy

You may have heard the poetic phrase, "Your baby's DNA lives in your bloodstream forever." To many, this evokes a sense of everlasting connection between mother and child. But what does the science say? This phenomenon, known as microchimerism, is a subject of growing research which is why Needed has enlisted Samantha Fessler, PhD, to delve into the studies and present research in an accessible way for those of us without a science degree.

Microchimerism: A complex memento of pregnancy

Throughout pregnancy, there is a transfer of fetal cells to the mother and maternal cells to the fetus via the placenta. Remarkably, these fetal cells can persist in the mother’s body for decades after pregnancy. This intriguing process underscores the profound biological ties between mother and child that endure well beyond the gestational period.

Yet, the implications of fetomaternal microchimerism for maternal and offspring health are still under scientific scrutiny. Current evidence reveals the intricate and multifaceted nature of this phenomenon, reminiscent of its mythological namesake—the chimera, in this article we will explore more about what this actually means.

What is Microchimerism?

Microchimerism describes the presence of cells within your body that originate from another genetically distinct individual. This happens via organ transplants, blood donations, or even pregnancy.

The term microchimerism owes its name to the fire-breathing creature of mythological origin, known as the chimera, composed of parts from three distinct animals: a goat, a lion, and a snake. 

How does the phenomenon of Microchimerism relate to pregnancy?

It is now well understood that biological transfer from mother to baby and vice versa, through the placenta, happens during pregnancy. While a mother passes oxygen, nutrients, and water among other critical substances to the fetus, the developing fetus traffics carbon dioxide and waste substances to the mother.

Compelling and ongoing research has also demonstrated that there exists placental exchange in both directions (mother to fetus, fetus to mother) of cells and DNA. 

The transfer of fetal cells across the placenta to the mother is called fetal microchimerism. While, the transfer of maternal cells to the fetus is referred to as maternal microchimerism. In fetal microchimerism, the fetal cells enter the maternal bloodstream and can integrate in maternal tissues.

Moreover, fetal cells have been shown to stick around in their maternal home for up to 3 decades following pregnancy. Importantly, the fetomaternal transfer of cells can begin to happen very early in pregnancy. With this, mothers may carry cells from their babies for a lifetime, even in cases of pregnancy loss.

Do These Fetomaternal Microchimeric Cells Play a Role in Maternal and Offspring Health?

As is the answer to many scientific questions, it’s complicated! Let’s dig in.

During pregnancy, a mother’s body adjusts so that the immune system does not sense the fetus as a non-self invader and mount an attack. So, these microchimeric cells help mother’s and baby’s bodies recognize and tolerate one another.

Also, when fetal cells are transferred and remain in the mother after a “healthy” pregnancy, this cellular “memory” may also help build a sort of resilience that reduces risk of adverse pregnancy outcomes in future pregnancies, such as preterm birth. Though, scientists think it is possible that mother’s immune system could remember adverse pregnancy outcomes as well.

As noted, fetal cells can circulate in the maternal bloodstream and are flexible in that they can form into a variety of tissues of the mother’s body. However, fetal microchimerism likely displays complexities in its effects on maternal health. These fetal cells, which stick around long after pregnancy, may play helpful, neutral, or adverse roles depending on a variety of factors – a focus of ongoing research! 

On the beneficial side, fetal cells may be transported in the maternal blood and assist in tissue repair at sites of injury using their ability to differentiate into a variety of cell types. For example fetal cells have been found in the incisions of cesarean sections, which likely point to how they help with wound healing. Another maternal tissue in which fetal cells can take up residence is the heart. Interestingly, mamas who experience heart attacks in late pregnancy or early postpartum time frames seem to have higher recovery rates than would be expected.

This has led many scientists to wonder if fetal microchimerism participates in the repair of heart tissue after cardiac events. In studies of pregnant mice, researchers found that fetal cells indeed travel to injured heart tissues after a heart attack. When these fetal cells migrate to the site of injury, they may differentiate into cells needed to repair mother's heart, such as heart muscle cells, which can aid in recovery of heart function.

Some research has found that fetal microchimerism may be related to autoimmune diseases such as rheumatoid arthritis and certain cancers in the mother. In some cases, fetal cells may be recognized as foreign invaders by the mother’s immune system. However, the transfer of fetal cells to the mother may be related to the reduction in autoimmune disease symptoms which is commonly experienced by mamas with these conditions during pregnancy. 

On the other hand, maternal cells from pregnancy which are maintained by their children may be related to success of organ transplants later in life from the mother as donor, compared to the father. Maternal microchimeric cells may also support immune system development in the fetus and improve their resilience in early life. Incredibly, maternal cells which stick around in female children may also support their healthy pregnancies in this generation’s reproductive years!

A fascinating recent study in mice highlighted the complexity of fetomaternal microchimerism and found that once a daughter does become pregnant, these maternal cell souvenirs seem to be replaced by the microchimeric cells of the developing fetus. 

Microchimerism - Memories of pregnancy and symbols of human connection

Fetomaternal microchimerism is a complicated phenomenon once thought to be a rare occurrence. However, ongoing research is shining a light on how these cellular exchanges between a mother and baby are common in human pregnancy and may function to influence maternal and offspring health.

The study of these microchimeric connections may also open doors which advance our understanding of how fetal cells interact with the maternal immune system and contribute to healthy versus high risk pregnancies – with potential to improve treatment strategies in the future.

For certain, this biological event tethers mama and baby through marvelous cellular memories that accentuate the natural wonders of this connection and our links to one another - as humans are all chimera.

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