At what point does parasympathetic maturation influence the fetal heart rate baseline?

At what point does parasympathetic maturation influence the fetal heart rate baseline?

• A. Parasympathetic activity increases causing a decrease in baseline heart rate with gestational age
• B. Parasympathetic activity increases causing an increase in baseline heart rate with gestational age
• C. Parasympathetic activity decreases baseline heart rate variability with gestational age
• D. Parasympathetic activity has no effect on heart rate with gestational age

Answer: (A)

Parasympathetic maturation increases vagal input to the SA node, slowing the intrinsic pacemaker rate. As gestational age advances, more parasympathetic fibers reach the heart and acetylcholine suppresses SA node firing, so the baseline fetal heart rate decreases. This is why the correct statement is that parasympathetic activity increases causing a decrease in baseline heart rate with gestational age. The other ideas don’t fit: vagal influence slows, not raises, the baseline rate; maturation typically brings greater vagal modulation and higher heart rate variability rather than decreasing it; and parasympathetic maturation does affect the baseline heart rate.

Parasympathetic maturation increases vagal input to the SA node, slowing the intrinsic pacemaker rate. As gestational age advances, more parasympathetic fibers reach the heart and acetylcholine suppresses SA node firing, so the baseline fetal heart rate decreases. This is why the correct statement is that parasympathetic activity increases causing a decrease in baseline heart rate with gestational age. The other ideas don’t fit: vagal influence slows, not raises, the baseline rate; maturation typically brings greater vagal modulation and higher heart rate variability rather than decreasing it; and parasympathetic maturation does affect the baseline heart rate.