How does oxygen transfer from maternal hemoglobin to fetal hemoglobin?

Oxygen transfer from maternal hemoglobin to fetal hemoglobin primarily occurs through passive diffusion. This process relies on the concentration gradient of oxygen between mother and fetus. Maternal blood, which has a higher concentration of oxygen, allows the oxygen to move across the placental barrier and into the fetal circulation, where the concentration is lower.

As fetal hemoglobin (HbF) has a higher affinity for oxygen compared to maternal hemoglobin (adult hemoglobin, HbA), it effectively binds the oxygen during this diffusion process. This efficient transfer is crucial for fetal development, especially given the relatively lower levels of oxygen available in the placenta compared to what the mother inhales.

While active transport and facilitated diffusion involve energy expenditure or specific carrier mechanisms, the transfer of oxygen in this context is a passive process due to simple concentration differences across the placental membranes. Hence, the most accurate description of how oxygen moves from maternal hemoglobin to fetal hemoglobin is through passive diffusion.