A 32-year-old primigravida woman at 20 weeks with blood group O positive and her husband has blood group AB positive. Which of the following is the most appropriate response to this patient's query that she and her husband have different blood groups and have already a pregnancy to deal with ?

ABO incompatibility typically occurs between a mother with blood group O and an infant with blood group A or B, which can cause mild hemolytic disease of the newborn. Affected infants are usually asymptomatic at bih or have mild anemia, and may develop neonatal jaundice that typically responds to phototherapy. The reasons only a MILD hemolysis are : (1) low prevalence of incompatible red cell antigens; (2) insufficient transplacental passage of fetal antigens or maternal antibodies; (3) maternal-fetal co existent ABO incompatibility, which leads to rapid clearance of fetal erythrocytes before they elicit an immune response; (4) variable antigenicity (5) variable maternal immune response to the antigen