So one of them is higher affinity of fetal hemoglobin for oxygen than the adult hemoglobin. The other is the fact that inside the blood of the mother, we have a higher concentration of oxygen than inside these capillaries of that fetus. And so because of this difference in concentration, because the concentration of oxygen is naturally higher inside the blood of that mother than inside the blood of that fetus, oxygen will tend to basically move down its concentration gradient, down its pressure gradient from the mother and to that fetus. So the final fact that that facilitates the diffusion of oxygen across our placenta is something called the double bore effect. So let's recall what a bore effect is. So, the bore effect is basically the ability of carbon dioxide to affect the affinity of hemoglobin.