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Scientists discover that even long after birth, a baby’s DNA remains in the mother’s body

By Cradlewise Staff

It’s common knowledge that mothers pass nutrition, DNA, cells, and immunity, among many other things, to their babies when they are in the womb. And as mothers often say, their babies are always a part of them. While many mothers say this figuratively, scientists have discovered that if you’ve physically given birth, it’s literally true as well: Some of your baby’s DNA will always be present in your body, even after delivery.

When a baby is in the womb, a part of their DNA moves to the mother’s body through the placenta and embeds itself in the mother’s tissues, becoming a permanent part of her. This is why mothers are made from not only their own genetic material, but also the genetic material of their children. Scientists call this occurrence microchimerism.

This phenomenon has lifelong consequences on the mother’s body and health. Read on to learn how and why it occurs.

What is microchimerism?

The term Microchimerism is formed from ‘micro,’ which here refers to the fact that the amount of cells exchanged is tiny, and ‘Chimera,’ a creature from Greek mythology that was part lion, part goat, and part serpent. Microchimerism means the presence of one or more genetically different cells in an organism.

Fetal maternal microchimerism refers to the transfer of the baby’s genetic material into the mother’s body long after the birth of the child. This transfer of fetal cells happens through the placenta and begins in the first trimester of pregnancy. When the baby’s cells from different pregnancies become a permanent part of the mother, it’s as though she becomes a chimera of sorts. 

We’ve known about the concept of passing cells from one body to another for more than a century now. In the womb, the mother’s cells pass to the baby through the placenta. Identical twins share a placenta and are also known to sometimes exchange microchimeric cells through it.

However, it was in 1979, for the first time, that researchers at Stanford University found some cells with Y sex chromosomes in a woman’s blood. Since women only have X chromosomes, the Y chromosomes were found to have come from her son, and transferred to her body during the pregnancy. This discovery marked the onset of further research in fetal microchimerism.

Did you know?
In 1996, Tufts University geneticist Diana Bianchi found male fetal cells in a mother’s blood 27 years after she had given birth.

What do the baby’s cells do in the mother’s body?

Once the baby’s cells cross the placenta and pass to the mother’s bloodstream, they circulate in her body and embed themselves in her tissues. Fetal cells are pluripotent like stem cells, meaning they can grow into different kinds of tissues and also help in tissue repair. After these cells embed themselves in the mother’s tissue, they grow into the same surrounding tissue by chemical interaction with the neighboring cells.

For example, in animal studies, it was found that when a mother rat’s heart was injured, the fetal cells migrated to her heart and differentiated into heart cells, helping repair the injury. 

Did you know?
In similar animal studies, it was also found that fetal cells migrated to the mother’s brain and transformed into nerve cells, integrating into her brain.

How does microchimerism affect the mother’s health?

A leading research paper on fetal microchimerism and maternal health in the journal BioEssays states that fetal cells are associated with “both positive and negative effects on maternal health.” While scientists are still figuring out the impact of fetal cells on human health, there is enough evidence to show that fetal cells actively participate in the mother’s health.

Fetal cells and Alzheimer’s

Scientists discovered cells containing the Y chromosome in the brains of deceased women. These cells were found in multiple regions of the brain and in more than 60 percent of brains. Multiple pregnancies have been found common in women with Alzheimer’s disease (AD). Because of this, scientists suspected that there would be a larger number of fetal cells in the brains of women with AD. The results were the opposite. The number of fetal cells in women with AD was much lower and scientists don’t know why.

Cancer

The jury is still out on this one. A study published in the American Association of Pharmaceutical Scientists, on understanding the role of fetal microchimerism in cancer states that “Microchimeric cells have been identified in healing and healed tissues as well as normal and tumor tissues. This has led to the hypothesis that fetal microchimerism may play a protective role in some cancers and may provoke other cancers or autoimmune diseases.”

But the presence of microchimeric cells in tumor tissues also indicates that they might be connected to tumor growth, so more research needs to be done about the connections between microchimerism and cancer.

Rheumatoid arthritis

In a study published in Arthritis and Rheumatism in 2010, scientists found that pregnancy provides vaccine-like protection against arthritis and rheumatism in women. For more than a century, doctors have been aware of the fact that arthritic pain reduces with pregnancy and resurfaces later. According to J. Lee Nelson, one of the study’s authors, “Protection starts about a year after birth, and then gradually attenuates after about 15 years.”

While the ongoing research will lead to more discoveries, we can relish in the knowledge that a part of our babies will always be with us.

FAQs

Q: How do cells transfer from the baby to the mother?

A: Cells and DNA transfer from the baby in the womb to the mother through the placenta.

Q: How long does microchimerism last?

A: It can vary, but fetal cells have been found to stay in the mother’s body for as long as decades after the birth of the baby.

Sources:

  1. Fetal microchimerism and maternal health. BioEssays. 2015. “Fetal microchimerism and maternal health: A review and evolutionary analysis of cooperation and conflict beyond the womb.”
  2. Multiple pregnancies. National Library of Medicine. 2006. “The number of pregnancies is a risk factor for Alzheimer’s disease.
  3. Fetal microchimerism in cancer. National Library of Medicine. 2015. Fetal Microchimerism in Cancer Protection and Promotion: Current Understanding in Dogs and the Implications for Human Health.”
  4. Rheumatoid arthritis. National Library of Medicine. 2010. “Does Pregnancy Provide Vaccine-Like Protection Against Rheumatoid Arthritis?
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