Microchimerism: One Reason Why You Feel So Weird During Pregnancy

If you're currently pregnant, or have been in the past, you may have experienced a strange sensation (and we're not talking about morning sickness!). Some women describe it as just "feeling different" – and the experience of your body feeling "different" or "weird" can continue even after giving birth.

One explanation for this is microchimerism: when two genetically distinct types of cells (i.e. your cells and your baby's cells) inhabit the same body. But why does this make us feel different, and why does it linger for months, and sometimes years after giving birth?

Let's break it down.

What exactly is microchimerism?

Back in 1979, researchers at Stanford University were surprised to find cells with Y sex chromosomes in a pregnant woman's blood. Since women only have X chromosomes, they figured the cells must have come from her fetal son.

During pregnancy, cells from both mother and baby travel back and forth across the placenta. This essentially makes them part of one another – and as much as 6% of free-floating DNA in a mother's blood comes from baby! Although this number drops significantly after birth, researchers understand that some cells may stick around, and evidence is showing they could actually have unique effects on mothers.

How common is it?

All pregnant women carry some amount of fetal cells in their blood, but in 1996, a geneticist named Diana Bianchi found male fetal cells in a mother's blood a whopping 27 years after she gave birth. We now know these cells can also travel to other parts of the body and become part of those tissues – so yes, that means your baby's cells can permanently become part of your own body!

In 2012, researchers studied the brains of women aged 32 to 101 and found that 60% had traces of male DNA from fetal cells in their brains. The oldest woman was an incredible 94 years old, showing us that a baby’s fetal cells could stay in mom’s body for her entire life.

At present, research is limited

Researchers study microchimerism by seeing if male DNA is present in the mother’s bloodstream or tissues. It’s easy to determine if a mother has fetal cells in her body by looking for a Y chromosome in women that have birthed male children since women should generally only have X chromosomes. Unfortunately, that means there's no easy way to distinguish a mother's cells from her daughter's – but generally, it's assumed that women who birth daughters can also experience microchimerism.

Because the research is still expanding and can generally only look into women that have birthed males, scientists don’t exactly know how many women are affected by microchimerism – but they are starting to believe it’s a lot more common than once thought.

What effects does microchimerism have on maternal health?

Scientists have been investigating if these fetal cells can help explain why pregnancy seems to offer both protective effects as well as increased health risks for mothers.

It’s known that motherhood reduces a woman’s risk for breast cancer, and studies have shown that mothers who are diagnosed with breast cancer tend to have lower levels of fetal cells in their blood than mothers who don't receive that diagnosis. Other recent studies have suggested these cells might actually offer a protective effect against autoimmune diseases. This leads us to wonder how the fetal cells work in our immune system, and if they can help the body better detect cancers.

But the jury is still out on the effects of microchimerism – we don’t exactly know if these cells are necessarily good or bad...

Fetal cells have also been found in some women’s cervical cancers, and not in the cervical tissue of women without this particular cancer. This might be because some fetal cells are actually stem cells, or have stem cell-like properties, which are great at reproducing. This can be really powerful for healing as stem cells can adapt into different types of tissues to provide for critical repair throughout one’s life, but, this proliferation (growth) potentially driven by these fetal cells might contribute to cervical cancer. It's a complicated area of study, and more research is needed, but you can read more on it here.

How long can these effects last?

When they first started studying microchimerism, researchers investigated the possibility of fetal cells having a connection to autoimmune diseases, since about 80% of people with autoimmune diseases are women.

Early theories suggested female sex hormones were the cause. However, if this was the case, these conditions should peak during a woman’s reproductive years when hormones are at their highest, but instead are typically diagnosed later in life.

It’s unclear how long microchimerism can affect a mother, but the evidence seems to be leaning towards a longer, more protective effect. The most common autoimmune disease is rheumatoid arthritis, and a 2010 study found the cells had a protective effect against the disorder. However, more research is needed to know what this really means for the future of women's health.

What does this mean for me?

You’ll most likely never know if you have these fetal cells (unless you were to get extensive genetic testing done, which is quite expensive!), so it's best not to worry about it what it might mean for you. These cells most likely have a purpose but more research is needed before we can confidently say whether they help or harm our bodies. However, pregnancy is part of the natural order, so it would make sense that our bodies have evolved to help protect that important function – and we're excited to see what the science has to tell us going forward! Ultimately, we hope this gives you even more evidence of how powerful and complex a woman's body is -- so you can better understand and appreciate the skin you're in.

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