Which factor can cause a decrease in fetal heart rate variability?

The use of certain medications is known to decrease fetal heart rate variability. Some medications, particularly those that act as sedatives or analgesics, can have a calming effect on the fetus, leading to a reduction in the variability observed in the fetal heart rate patterns. Medications like narcotics or magnesium sulfate, for instance, can impact the autonomic nervous system's control over the heart, resulting in a more stable heart rate with less variability.

In contrast, improved maternal hydration typically enhances placental perfusion, which can lead to better oxygenation and potentially increased fetal heart rate variability. Increased fetal activity generally corresponds with heightened fetal heart rate variability, as movement stimulates changes in heart rate patterns. A change in maternal position can also affect blood flow to the placenta and the fetus but does not inherently lead to decreased variability; rather, it may have neutral or variable effects depending on the situation. Understanding these interactions is crucial for assessing fetal well-being during monitoring.