Blood transfusions
Generally, when giving a blood, the sex of a blood donor considered irrelevant. A new study suggests, blood transfusions delivered to men using blood from previously pregnant women could increase their risk of dying in the years following the transfusion.
Dr. Rutger Middelburg, from Sanquin Research in Leiden, said, 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.
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.
Scientists used computer modeling techniques to improve blood flow in veins
An alternative explanation could be a difference in iron status between ever-pregnant female and male donors. Some studies report differences in red blood cell physiology between the sexes.

Researchers analyzed death rates among 31,118 patients who received 59,320 red blood cell transfusions in between 2005 and 2015. In total, nearly 4,000 patients died after giving blood.
Research results
These results identified only in men under the age of 50. It seems if a man over the age of 50 he is immune to whatever specific risk factor present in the blood of a formerly pregnant female donor.
From all the men contributing to 1,000 years-worth of study, there were 101 deaths after transfusion from an ever-pregnant donor compared with 80 after receiving blood from a male donor. Women donors who had never been pregnant associated with only 78 male deaths per 1,000 person-years.
Researchers said, this is an observational study, and it always difficult to establish what causes what in such studies. Maybe there is some difference between men who received blood from women who pregnant. Men who received blood from other donors that has nothing to do with the source of the blood they received.
More information: [The JAMA Network]