Maternal-fetal ABO/Rh antigenic relationships and human fetal development.

Six hundred ninety-nine primigravid mothers and their neonates were grouped into three distinct classes on the basis of maternal-fetal antigenic relationships for the ABO and Rh blood groups. Maternal-fetal units were classified as maternal dominant if the mother possessed more antigens than the neonate, equivalent if both possessed the same number of antigens, and fetal dominant if the neonate possessed more antigens than the mother. After confounding variables were controlled, a significant increase in adjusted mean birth weight was observed from maternal-fetal equivalence to fetal dominance and there was a significant increase in adjusted crown-heel length from maternal dominance to fetal dominance. No trends were observed for adjusted head circumference. However, when the sample was stratified on the basis of sex of the neonate, a highly significant increase in adjusted mean head circumference was observed for female infants from maternal dominance through fetal dominance. These observations suggest maternal-fetal ABO/Rh relationships are associated with differential fetal growth trends.