<prompt> Which Antibody crosses placenta?IgG1IgG4IgAIgD  <response>: Ans. a IgG1Ref: Maternal, Fetal, Neonatal Physiology: A Clinical Perspective; pg 484All four IgG subclasses cross, although the IgG1 and IgG3 subclasses are predominate.IgG1 crosses earliest in pregnancy is the primary immunoglobulin transferred before 28 weeks.IgG3 crosses later does not reach maternal levels until after 32-33 weeks 