A 28-year-old woman, gravida 2 para 2, brings her healthy 6-day-old girl to the office for her first well-baby checkup. The infant was born full-term, with a birth weight of 4.2 kg (9.3 lb) and a length of 51 cm (20 in). She was discharged from the nursery with no concerns. Physical examination is normal. The infant's blood type is A negative, whereas the mother's is B negative. High circulating levels of anti-A antibodies are found in the mother's blood. Hemolysis did not occur in the infant because these maternal antibodies are most likely of which class?
RBC antibody screen | ||
Maternal blood group | Maternal RBC antigens | Maternal serum antibodies |
A | A antigen | Anti-B (IgM) |
B | B antigen | Anti-A (IgM) |
AB | A and B antigen | None |
O | None | Anti-A and Anti-B (IgM and IgG) |
RBC = red blood cell. | ||
Hemolytic disease of the fetus and newborn (HDFN) is caused by maternal anti-fetal erythrocyte IgG antibodies, which can cross the placenta and produce a type II (antibody-mediated) hypersensitivity response. With maternal blood types A or B, hemolysis (eg, erythrocyte destruction) does not occur because the maternal antibodies (anti-A or anti-B) are of the IgM type, which cannot cross the placenta. However, mothers with blood type O also produce IgG antibodies which can cause hemolysis in the fetus.
The association of a fetus with blood type A or B and a mother with blood type O occurs in approximately 15% of pregnancies; however, HDFN occurs in only 3% of these pregnancies due to variations in fetal ABO antigen expression. Unlike Rh disease, HDFN can occur with the first pregnancy because anti-A and anti-B antibodies are formed early in life from exposure to A- or B-like antigens present in foods, bacteria, and viruses.
(Choice A) IgA plays an important role in mucosal immunity and is found in high amounts in colostrum. The secretory IgA provided by the mother's breast milk coats the infant's intestinal mucosa and provides protection from ingested pathogens.
(Choice B) IgD is an immunoglobulin of unclear significance. It is often concurrently expressed with IgM on the membranes of B lymphocytes and is believed to act as a cell surface antigen receptor for those cells.
(Choice C) IgE is the immunoglobulin most notably responsible for atopic diseases such as asthma, atopic dermatitis, and allergic rhinitis. It also plays a role in defense against helminth parasites.
(Choice D) IgG crosses the placenta and remains circulating in the bloodstream of infants, providing them with passive immunity for up to 6 months.
Educational objective:
With maternal blood types A or B, hemolytic disease of the fetus and newborn very rarely occurs because maternal antibodies (anti-A or anti-B) are of the IgM type and cannot cross the placenta. In contrast, mothers with blood type O also produce IgG antibodies (anti-A and anti-B), which can cross the placenta and cause fetal hemolysis.