Blood bags containing O negative blood for neonate (newborn) babies and infants. Babies need less blood than adults, so only 55ml of blood is in these bags, about four times smaller than the volume of an adult blood bag. The donor blood has been through a process of separation and mixing of its component parts to optimise its use. The blood group and type needs to be matched to that of the baby in need. Infant blood transfusions are mainly used to replace lost blood due to an injury or during surgery.