A neonate born at 28 weeks who has not had a blood transfusion and is now 12 weeks postnatal age should have approximately what percentage of fetal hemoglobin?

• A. 30%
• B. 100%
• C. 70%
• D. 90%

Answer: (C)

Fetal hemoglobin (HbF) persists longer in preterm infants, and the switch to adult hemoglobin (HbA) happens more slowly as gestational age decreases. After birth, HbF gradually declines as gamma chains are replaced by beta chains, but in a baby born at 28 weeks this process is delayed compared with term infants. By about 3 months after birth, a very preterm infant typically still has a high HbF fraction, around seventy percent, since HbA has not yet become the majority.

Therefore, at 12 weeks postnatal age with no transfusion, about 70% HbF is expected. Transfusions would introduce HbA-containing cells and could reduce the HbF percentage, but in this scenario the natural persistence of HbF is the deciding factor.