Chemoreceptor stimulation due to high CO2 leads to which fetal heart rate change?

• A. Increase in HR
• B. Decrease in HR
• C. No change
• D. Variable change

Answer: (B)

Elevated CO2 stimulates fetal chemoreceptors, which triggers increased vagal (parasympathetic) activity to the heart. This slows the sinoatrial node and causes a decrease in fetal heart rate (bradycardia). In fetal distress, rising CO2 and acidosis shift the response toward slower heart rates to protect tissues, rather than speeding the heart. Early hypoxia can briefly raise heart rate due to sympathetic activation, but when chemoreceptors are stimulated by high CO2, the dominant effect is bradycardia.