NCC Certified Electronic Fetal Monitoring (C-EFM) Practice Exam

What factor most significantly influences FHR variability?

1. Fetal movement

2. Cerebral oxygen and intact CNS

3. Maternal heart rate

4. Amniotic fluid volume

The correct answer is: Cerebral oxygen and intact CNS

Fetal heart rate (FHR) variability is primarily influenced by the central nervous system (CNS) of the fetus and its ability to respond to various internal and external stimuli. An intact CNS, particularly involving normal cerebral oxygenation, plays a critical role in regulating FHR variability. When the fetus is well-oxygenated, the CNS can effectively facilitate the balance between sympathetic and parasympathetic nervous system activity, resulting in appropriate fluctuations in the heart rate. On the other hand, factors like fetal movement and maternal heart rate can certainly have some adaptive effects on FHR, but they are not the primary drivers of variability. Fetal movement is generally associated with short-term accelerations in the FHR but does not fundamentally change the overall variability. Similarly, maternal heart rate might influence blood flow to the fetus, but it does not directly impact the variability of the fetal heart rate. While amniotic fluid volume can affect fetal well-being, its relationship with FHR variability is more indirect, as it can influence parameters like compression of the umbilical cord rather than the central nervous system's function. In summary, intact cerebral oxygenation and a functioning CNS are critical for maintaining healthy FHR variability, making this the most significant influencing factor.