Newborns with a heart defect may have two strikes against their future health, rather than one.

Babies with heart birth defects appear to have a higher risk of developing childhood cancer, compared to those without a heart abnormality, researchers report in the journal Circulation.

Childhood cancers are 66% higher in newborns with a congenital heart defect, compared to those born with healthy hearts, researchers say.

Further, cancer risk was more than double in newborns with heart defects that included blood vessels or heart valves, and twice higher among those with complex defects, results show.

“The genetic variants inherited from the mother may provide the necessary environment for cancer to develop in congenital heart defect patients, highlighting a possible shared genetic pathway underlying both conditions,” senior researcher Dr. June Huh, a professor of cardiology at Sungkyunkwan University School of Medicine in Seoul, South Korea, said in a news release.

In the U.S., about 12 in every 1,000 births involve a congenital heart defect, researchers said in background notes.

For the study, researchers analyzed more than 3.5 million live births that occurred in South Korea between 2005 and 2019, following all newborns for an average of 10 years.

Newborns with valve or vessel problems were 2.3 times more likely to develop cancer later in childhood, and those with complex heart defects 2 times more likely, results show.

That cancer risk extended to moms as well, researchers noted.

Mothers of children with heart defects had a 17% higher risk of cancer, results show.

“This finding needs to be further explored to understand if there are environmental factors affecting genes (epigenetics) or stress-related changes linking congenital heart defects with maternal cancer risk,” American Heart Association expert Dr. Keila Lopez said in news release.

“There is some data that suggests stress is related to cancer risk, and having a child with a congenital heart defect can be very stressful,” said Lopez, an associate professor of pediatric cardiology at Texas Children’s Hospital in Houston. “So having studies that investigate and demonstrate all the links between cancer and congenital heart defects will help us understand lifelong risks of not only heart defects but also the development of cancer within families.”