Which statement correctly describes differences between fetal and maternal blood during labor?

Which statement correctly describes differences between fetal and maternal blood during labor?

• A. Fetal blood has a lower hemoglobin concentration than maternal blood
• B. Fetal placental blood flow is twice maternal placental blood flow
• C. Fetal hemoglobin has a greater affinity for oxygen than maternal hemoglobin
• D. The fetal oxyhemoglobin dissociation curve is shifted to the right of the maternal curve

Answer: (C)

The key idea is that fetal hemoglobin binds oxygen more tightly than maternal hemoglobin, which facilitates pulling oxygen from maternal blood across the placenta. Fetal hemoglobin (with its gamma chains) has a reduced interaction with 2,3-BPG, so its oxyhemoglobin dissociation curve lies to the left of the maternal curve. This leftward shift means that at the same partial pressure of oxygen, fetal hemoglobin is more saturated, enabling efficient loading of oxygen in the placenta even when fetal PO2 is lower. That higher oxygen affinity is why fetal blood can take up O2 from maternal blood effectively during labor and throughout gestation. The other statements don’t match this physiology: fetal hemoglobin concentration isn’t categorically lower than maternal, placental blood flow isn’t defined as a specific multiple of maternal flow, and the fetal curve is not shifted to the right but to the left.

The key idea is that fetal hemoglobin binds oxygen more tightly than maternal hemoglobin, which facilitates pulling oxygen from maternal blood across the placenta. Fetal hemoglobin (with its gamma chains) has a reduced interaction with 2,3-BPG, so its oxyhemoglobin dissociation curve lies to the left of the maternal curve. This leftward shift means that at the same partial pressure of oxygen, fetal hemoglobin is more saturated, enabling efficient loading of oxygen in the placenta even when fetal PO2 is lower. That higher oxygen affinity is why fetal blood can take up O2 from maternal blood effectively during labor and throughout gestation. The other statements don’t match this physiology: fetal hemoglobin concentration isn’t categorically lower than maternal, placental blood flow isn’t defined as a specific multiple of maternal flow, and the fetal curve is not shifted to the right but to the left.