Medical Emergencies · single question
What is the most likely Rh blood type of a child at risk for Erythroblastosis Fetalis when the mother is Rh-negative (O-) and the father is Rh-positive (A+)?
Show answer and explanation
Correct answer: A. O+
Erythroblastosis fetalis (hemolytic disease of the newborn) occurs when an Rh- mother carries an Rh+ fetus. The mother's anti-Rh antibodies cross the placenta and attack fetal RBCs. The father is A+ — he may pass either the A antigen or O (blood type) AND either Rh+ or Rh-. A child at RISK must be Rh+ (to trigger maternal sensitization). The child could be O+ (received O from mother, Rh+ from father) or A+ (received A from father, Rh+ from father). A (O+) is the most straightforward answer since mother is O-, child gets O from her and Rh+ from father.
- A. Correct. Erythroblastosis fetalis (hemolytic disease of the newborn) depends on the Rh(D) antigen, not on ABO type. An Rh-negative mother sensitized to D antigen produces IgG anti-D, which crosses the placenta and hemolyzes fetal RBCs in any Rh-POSITIVE fetus. From this cross the child may be O or A, and Rh-positive or Rh-negative — every Rh-POSITIVE outcome is at risk. RhoGAM (anti-D immunoglobulin) prevents maternal sensitization.
- B. A+ is Rh-positive and at risk — but again not the only possibility.
- C. An Rh-NEGATIVE child is not at risk; there is no Rh antigen for maternal anti-D antibodies to attack.
- D. O+ is Rh-positive and is at risk — but it is not the only at-risk type from this cross.
Practice Medical Emergencies questions Medical Emergencies study notes