Relative affinity of human fetal hemoglobin for carbon monoxide and oxygen.

T HE RATIO OF CARBON MONOXIDE ( CO) to oxygen bound by hemoglobin A is 217 times greater than the ratio of these gas tensions in the equilibrium medium.’ This report shows that hemoglobin F has less preferential binding of CO over 02 than hemoglobin A. Because of this difference between adult and fetal hemoglobin the diffusion gradient for CO across the placenta can not be equated with the difference in carboxyhemoglobin per cent saturation ( COHb ) . This relationship is of interest when comparisons are made between maternal and fetal COHb levels to determine the direction of CO transfer. Such comparisons are pertinent when CO is used to evaluate placental function,2 and when CO is implicated as mcdiating an adverse effect on the fetus from maternal smoking.3’4