Which of the following is NOT a cause of fetal bradycardia?

Which of the following is NOT a cause of fetal bradycardia?

• A. Hypoxemia
• B. Acidosis
• C. Neostigmine and glycopyrrolate reversal of neuromuscular blockers
• D. Maternal smoking

Answer: (D)

Fetal bradycardia reflects distress from reduced oxygen delivery to the fetus or direct cholinergic effects on the fetal heart. When oxygen delivery falls, the fetus initially responds with tachycardia, but as hypoxia and acidosis worsen, parasympathetic (vagal) activity dominates and the heart rate falls. Acidosis further depresses cardiac performance, making bradycardia more pronounced. The reversal of neuromuscular blockade with neostigmine can provoke fetal bradycardia because neostigmine increases acetylcholine, and glycopyrrolate is given to block maternal muscarinic effects. The drugs can cross the placenta and stimulate the fetal heart via muscarinic receptors, slowing the rate. Maternal smoking, while it can contribute to chronic placental insufficiency and fetal hypoxia over time, does not cause an acute, direct fetal bradycardia event in the same way. It’s a risk factor for adverse fetal outcomes, but it isn’t a direct immediate mechanism producing bradycardia during anesthesia or surgical scenarios.

Fetal bradycardia reflects distress from reduced oxygen delivery to the fetus or direct cholinergic effects on the fetal heart. When oxygen delivery falls, the fetus initially responds with tachycardia, but as hypoxia and acidosis worsen, parasympathetic (vagal) activity dominates and the heart rate falls. Acidosis further depresses cardiac performance, making bradycardia more pronounced.

The reversal of neuromuscular blockade with neostigmine can provoke fetal bradycardia because neostigmine increases acetylcholine, and glycopyrrolate is given to block maternal muscarinic effects. The drugs can cross the placenta and stimulate the fetal heart via muscarinic receptors, slowing the rate.

Maternal smoking, while it can contribute to chronic placental insufficiency and fetal hypoxia over time, does not cause an acute, direct fetal bradycardia event in the same way. It’s a risk factor for adverse fetal outcomes, but it isn’t a direct immediate mechanism producing bradycardia during anesthesia or surgical scenarios.