Carbon monoxide: effects on oxygenation of the fetus in utero.

The partial pressure of oxygen in fetal blood decreases in proportion to the carboxyhemoglobin concentrations in fetal and maternal blood. Because fetal oxygen tensions normally equal 20 to 30 percent of the values for adults, this reduction can result in severe hypoxia of vital tissues. Decreases in oxygen tension may be a factor in the lower birth weights of infants born to women who smoke or are exposed to severe air pollution.