ABO and bacterial infectious disease: If potentially protective IgG antibodies can be transferred from the pregnant individual to the fetus—such as the case when mother and offspring have dissimilar (ie, incongruent) ABO blood groups (eTable 1 in Supplement 1)—then a logical question is, does maternal-fetal ABO blood group incongruence confer a lower risk of bacterial infection on the newborn than maternal-fetal ABO blood group congruence?