According to a new study, men under 50 are 1.5 times more likely to die three years after a transfusion if the blood injected into their system came from a woman donor who, at one point, had been pregnant.

Blood transfusions are typically a matter of matching blood types, but this new study raises questions about risks in blood compatibility and suggests that there might be a need for health institutions to reevaluate the importance of matching sexes when it comes to blood transfusion.

Men Are More Likely To Die After Receiving Blood From Women Who Were Pregnant

According to the study, which was published Tuesday, Oct.17, in the The Journal of the American Medical Association, men transfused with blood from previously pregnant women are more likely to die in the coming years compared with those who were transfused with blood from a man. Female recipients, meanwhile, did not appear to face the same risks. The study looked at more than 30,000 transfusion patients in the Netherlands, as New Atlas reports.

"The risk remained increased for many years after transfusion. No such increase was observed for female recipients, or for male recipients over 50 years," said Merlijn van Hasselt. She is a spokesperson for Sanquin, which is "responsible for safe and efficient blood supply in the Netherlands on a not-for-profit basis," says its website.

More Studies Needed

Why is this so? According to Van Hasselt, a woman's pregnancy might ultimately affect her immune system, and this somehow makes her blood riskier for a man to receive.

Both the researchers and the American Red Cross were quick to warn that the study isn't definitive enough to cause a shift in the way blood transfusions are currently matched. However, if future studies give more credence to this new discovery, it could singlehandedly alter the way hospitals and health care facilities validate blood transfusions, and more importantly, it could mean that countless transfusion patients around the world have died without knowing this newfound risk.

This could lead to a global-scale change, but more studies need to be performed.

"It needs to be followed up," said Dr. Louis Katz, chief medical officer of America's Blood Centers.

It's quite odd that men over 50, as the study notes, seem to be immune to whatever specific risk factor is present in the blood of a woman who had been pregnant in the past. Again, more follow-up research is needed to determine lots of factors, but this discovery is already pretty alarming.

Does Sex Matching Matter In Blood Transfusions?

There are conflicting reports about the risks of blood transfusions between different sexes. Gustaf Edgren, for one, believes there is no correlation between the sex of the donor and the mortality of the recipient, and age seems to be meaningless component as well. In June, he published his findings in The Journal of the American Medical Association.

Another scientist, Henrik Bjursten, looked at 10,000 patients in a 2016 study and found the results to be opposite of Edgren's, concluding that transfusions between men and women do increase mortality risks. He believes that same-sex blood transfusions should already be widely implemented.

The authors of the new study think that a certain antibody formation that occurs during pregnancy could be the culprit of increased mortality rates for men. Why, though, does it only affect men under 50 and not women? It remains largely uncertain.

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