ABSTRACT
Fifty-four intrapartum fetal heart rate (FHR) tracing were subjected to retrospective
analysis of the presence, length, and frequency of cyclic changes in long-term variability
(cyclicity). All patients had spontaneous uncomplicated labor and received no narcotics
or analgesics. The following cycles were identified according the difference in long-term
variability in terms of amplitude range: cycle A, 0 to 2.5 beats/min; cycle B, 3 to
5 beats/ min; cycle C, 6 to 10 beats/min; and cycle D, 11 to 20 beats/min. The frequency
and length of FHR cycles was established in the latent, active phases and second stage
of labor. Periods of diminished variability should be followed by fetal acid-base
assessment only if their duration exceeds the established norms.
