 Carbon monoxide poisoning in pregnant women may cause severe adverse fetal effects . Poisoning causes fetal tissue hypoxia by decreasing the release of maternal oxygen to the fetus . Carbon monoxide also crosses the placenta and combines with fetal hemoglobin , causing more direct fetal tissue hypoxia . Additionally , fetal hemoglobin has a 10 to 15 % higher affinity for carbon monoxide than adult hemoglobin , causing more severe poisoning in the fetus than in the adult . Elimination of carbon monoxide is slower in the fetus , leading to an accumulation of the toxic chemical . The level of fetal morbidity and mortality in acute carbon monoxide poisoning is significant , so despite mild maternal poisoning or following maternal recovery , severe fetal poisoning or death may still occur . 
