Fluctations in the fetal heart rate, recorded by the electronic monitor, that reflect the status of the fetal autonomic nervous system. Absence of short-term variability (beat-to-beat changes) is a sign of fetal compromise. Long-term variability (wavelike undulations) occurs normally three to five times per minute. Increased long-term variability is common during fetal sleep but may reflect prematurity, congenital abnormalities such as anencephaly, or fetal response to drugs.