I use to work at the Red Cross doing the traveling bloodmobiles. Its been a few years (approx. 6-7) but I doubt the rules have changed. No donating while pregnant or nursing because you need your own blood to nourish your baby. If you are low the baby will be too. I know that no donation during pregnancy makes sense to most. But, during breastfeeding is definately a great question! If you are compromised (from donating) then your body will have a harder time producing the milk it needs for baby. Remember that a big majority of your blood content is water too. So thats probably the main reason they don't allow it!