A mother and her baby are never physically closer than during pregnancy — and a new study has demonstrated that this close relationship lasts long after pregnancy, with powerful health benefits.

During pregnancy, it’s well known that mothers and babies share cells and DNA material. A group of Danish researchers has shown that remnants of this genetic material can persist in the mother’s body for life and confer long-lasting health benefits. Amazingly, women who tested positive for fetal DNA in their blood had a 60 percent lower mortality rate, primarily because of dramatically reduced cancer rates when compared to women who didn’t have this remnant DNA, according to the study published in the International Journal of Epidemiology.

This condition is known as microchimerism, named after the Greek myth of the chimera, a fire-breathing monster with the head of a lion, the body of a goat, and the tail of a serpent.

To test for microchimerism, the team of Danish researchers analyzed the blood of women enrolled in the Danish Diet, Cancer and Health study. They found leftover male DNA in approximately 70 percent of women, then they followed this group for long-term health outcomes. All pregnant women carry some fetal cells and DNA, with up to 6 percent of the free-floating DNA in the mother’s blood plasma coming from the fetus.

The researchers tested for male DNA because it’s easier and less expensive to detect Y chromosomes (male chromosomes) in female blood than trying to detect X chromosomes (female chromosomes) from daughters. One of the study authors, Mads Kamper-Jorgensen, an associate professor of public health at the University of Copenhagen, noted there was no difference in health outcomes between mothers of sons and daughters when it comes to microchimerism.

“Sons are no better than daughters,” he told the Atlantic.

Microchimerism was discovered in 1979, when researchers at Stanford discovered male DNA in a mother’s blood and realized the cells had come from her son. Since then, researchers have been studying what, if any, effect microchimerism has on mothers and their children. This new study adds new support (though the sample size in the study is low) to findings that microchimerism may support the mother’s healthy immune system, reducing the risk of cancer (e.g., breast and ovarian) and autoimmune diseases like rheumatoid arthritis.


  • During pregnancy, mothers and babies share cells and DNA material, a condition known as microchimerism.
  • Danish researchers found leftover male DNA in approximately 70 percent in a study of 272 women.
  • Microchimerism may reduce the risk of cancer and autoimmune diseases.

Last reviewed by Jennifer Lincoln, MD, IBCLC. Review Date: January 2019


  1. International Journal of Epidemiology. Male microchimerism and survival among women.
  2. Scientific American. Beyond birth: A Child’s Cells May Help or Harm the Mother Long After Delivery.
  3. The Atlantic. Your Baby’s Leftover DNA Is Making You Stronger.


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