If you’re really into learning how the body works, and how your physiology changes during pregnancy, you might be asking: What is the deal with blood donation in relation to pregnancy? You learned after all, that that as your womb grows, as the fetus grows, eventually you have a much large blood supply than you normally do. Generally, blood volume increases by about 60 percent. This raises a question of whether pregnant women should be considered as a source for blood donation.
It’s not so simple though, because it turns out that you, and your fetus, actually need the extra blood. All of it –at least enough of it, such that the Red Cross and other agencies would get very nervous seeing a pregnant woman walk in to donate. The guidelines do not permit it. They will not accept you. End of discussion.
If you offer to donate, they’ll defer you and tell you to return at least a few months after you give birth. Then, you’ll be like the rest of us and simply have to pass a host of other requirements, which can be grueling and in some cases frustrating. Along with many other Americans, for instance, I spent more than three months in the United Kingdom prior to 1996. Today that is disqualifying if you want to give blood in the US, though I qualified several years ago when cutoff was six months. They are worried about prions, little misbehaving proteins that cause terrible brain diseases, and which there is no reliable way to detect in blood. The prions are a risk, because of an epidemic of mad cow disease that was not put into check until 1996, so the concern is that donors could have risky blood on account of eating the British beef. It doesn’t matter to the Red Cross that I actually never ate beef when I was doing my exchange program in England. I exceeded three-month limit in being there, and so, in order to donate blood in the US, I have until the science for screening blood of prions advances.
Synthetic blood might be perfected by that time, but if you have not been in Europe before 1996, and if you have no other risk factors, you’ll only have to wait until your body is out of pregnancy mode.
Donation by mothers, especially those who have been pregnant multiple times, could put some blood recipients at risk. That’s because of a rare (estimated 1 out of 5,000 transfused units) but serious complication, called transfusion-related acute lung injury (TRALI). By definition, TRALI develops within six hours of transfusion. It involves an immune system reaction causing life-threatening changes in the lungs. Possibly, the trigger comes from antibodies present in the plasma component of donated blood products, antibodies that are hypothesized to be generated by the immune system due to multiple contacts between the donor’s blood and the blood of her fetuses. If this hypothesis is correct, then the mechanism is similar to what happens in what’s called Rh incompatibility, the pregnancy complication that occurs when a mother with Rh-negative blood is exposed to Rh-positive blood from a first fetus, and then is exposed again because of a second Rh positive fetus, when her immune system reacts more strongly. In Rh incompatibility, the problem can be prevented by giving the mother an antibody called RhoGAM. With TRALI, on the other hand, there is no way to prevent the reaction yet, and the victim is not a fetus, but a blood product recipient with no connection to the donor.
Now, generally, the danger of TRALI comes in with donated plasma. That’s the liquid component of blood after the blood cells are removed. Though it lacks cells, the plasma contains proteins, including antibodies. Theoretically, the red blood cells (RBCs) from such a donor should not provoke TRALI, since RBCs are separated from plasma and cold-preserved as packed RBCs (PRBCs). Patients are not given whole blood as they were in in the past. Consequently, blood donation guidelines discourage women who have been pregnant many times from donating plasma, but do not discourage donating blood, since the PRBCs are thought to be safe. Still, there have been a small number of published cases of TRALI in patients after receiving PRBCs, probably due to remnants of plasma persisting with the RBCs as they were packed and stored.
