In a healthy newborn, hemoglobin F makes up roughly what proportion of total hemoglobin?

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Multiple Choice

In a healthy newborn, hemoglobin F makes up roughly what proportion of total hemoglobin?

The key idea is that newborns have hemoglobin that is predominantly fetal type. Fetal hemoglobin (HbF) is produced by the fetus and has a higher affinity for oxygen, which helps with oxygen transfer before birth. In a healthy term newborn, HbF typically makes up the majority of total hemoglobin—roughly from sixty percent up to about ninety percent—while HbA accounts for the remaining roughly ten to forty percent. This big HbF fraction reflects the ongoing switch from fetal gamma chains to adult beta chains after birth. Over the next several months, HbF declines as HbA increases, and by about six months of age HbF is largely replaced. The other patterns imply an adult-like distribution or too little HbF for a newborn, which isn’t consistent with normal newborn physiology.

The key idea is that newborns have hemoglobin that is predominantly fetal type. Fetal hemoglobin (HbF) is produced by the fetus and has a higher affinity for oxygen, which helps with oxygen transfer before birth. In a healthy term newborn, HbF typically makes up the majority of total hemoglobin—roughly from sixty percent up to about ninety percent—while HbA accounts for the remaining roughly ten to forty percent. This big HbF fraction reflects the ongoing switch from fetal gamma chains to adult beta chains after birth. Over the next several months, HbF declines as HbA increases, and by about six months of age HbF is largely replaced. The other patterns imply an adult-like distribution or too little HbF for a newborn, which isn’t consistent with normal newborn physiology.

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