Men who receive blood transfusions are more likely to die if their donor is a woman who has been pregnant, according to new research.

The study, which analysed 10 years’ worth of data, found that male recipients under the age of 50 were 1.5 times more likely to die after a transfusion from a pregnant woman - which represents a six per cent increase in mortality.

Researchers analysed death rates among 31,118 patients in the Netherlands, and found that nearly 4,000 of this group - or 13 per cent - died after receiving blood, according to a report in The Telegraph.

One of the most common causes of death was transfusion-related acute lung injury (TRALI), a rare but serious side effect of receiving blood which causes respiratory distress.

“Male recipients who received a transfusion from an ever-pregnant female donor had a statistically significant increase in mortality compared with those who received a transfusion from a male donor or from a female donor without a history of pregnancy”, wrote Dr Rutger Middleburg in the Journal of the American Medical Association.

“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.

“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.

“Further research is needed to replicate these findings, determine their clinical significance, and identify the underlying mechanism.”

However, a spokesperson for NHS Blood and Transplant told The Telegraph the study did not conclusively prove blood donations from women who had been pregnant necessarily posed a risk to male recipients.

"As the authors of this study have made clear, further research is needed to determine if it’s finding have any clinical significance.

"Blood donations from all our donors are lifesaving, and we continue to encourage donations from women who have previously been pregnant.