Men who receive blood transfusions from women who have been pregnant are more likely to die, a study has found. Scientists from Sanquin Research found that transfusions from blood donors who have been pregnant were associated with an increased risk of mortality in male recipients, but not female recipients.

The study looked at 31,118 patients who had received 59,320 red blood cell transfusions between 2005 and 2015 in major hospitals in the Netherlands. By comparing survival rates of the recipients, they found "a statistically significant increase in all-cause mortality among male recipients of red blood cell transfusions".

In total, 3,969 patients studied died after their transfusions, with the lead cause being transfusion-related acute lung injury.

The researchers found that men under the age of 50 were 1.5 times more likely to die within three years, if they received a transfusion from a woman who had been pregnant before donating.

Whilst significant, this isn't a huge increase, but nevertheless, it could have implications for transfusions in the future if the same results are replicated elsewhere. The same results were not seen in female recipients of blood transfusions, and their mortality was not affected in any statistically significant way. Their results are published in the Journal of the American Medical Association.

Further study is needed, and the National Health Service in the UK have stated that they continue to welcome donations from women who have been pregnant. Shutterstock.

The researchers suggested that this increase in risk of mortality could be due to antibodies acquired during pregnancy.

“The association of increased mortality among male patients who received transfusions from ever-pregnant donors suggests a possible mechanism based on immunologic changes occurring during pregnancy," Dr Rutger Middelburg from Sanquin Research said, reports the Telegraph.

“An alternative explanation could be a difference in iron status between ever-pregnant female and male donors. Some studies also report differences in red blood cell physiology between the sexes."

The authors point out that further research is needed "to replicate these findings, determine their clinical significance, and identify the underlying mechanism.”

"These results are provocative and may – if true – have significant clinical implications," Ritchard G Cable MD wrote in an editorial on the JAMA Network. However, he urged caution, and stated that other clinical trials have had different results.

The National Health Service in the UK told the Telegraph that blood donations from all donors were welcome and that they continue to welcome donations from women who have been pregnant.