What is the effect of carbon monoxide exposure on fetal oxygen delivery?

• A. Inactivates maternal and fetal hemoglobin, decreasing oxygen carrying capacity
• B. Increases oxygen carrying capacity
• C. Has no effect on hemoglobin
• D. Improves fetal oxygenation

Answer: (A)

Carbon monoxide reduces fetal oxygen delivery by binding to hemoglobin and forming carboxyhemoglobin, which lowers the blood’s oxygen-carrying capacity. CO binds hemoglobin far more readily than oxygen, so less O2 can be carried in both maternal and fetal blood. The remaining hemoglobin also holds onto oxygen more tightly, shifting the dissociation curve to the left and making it harder to release oxygen to fetal tissues. Because CO crosses the placenta, carboxyhemoglobin forms in the fetal circulation as well, compounding the effect. The overall result is decreased oxygen delivery to the fetus, leading to fetal hypoxia.