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?

Question

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?

Quizplus · Accepted Answer

Eductional 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.

A 28-Year-Old Woman, Gravida 2 Para 2, Brings Her Healthy