Two issues important in the interpretation of an FHR record are the classification of FHR variables and interobserver reliability in the visual interpretation of these variables.
Many definitions of the individual FHR variables, baseline FHR, baseline FHR variability, accelerations and decelerations have been provided. A good example is provided in the RCOG Evidence-based Clinical Guideline Number 8. However differences of classification criteria remain, particularly for decelerations. In the classification of late decelerations, some clinicians have given first priority to the timing of the nadir of the deceleration, whereas others have emphasized the waveform. In the interpretation of the waveform, both the onset to the nadir  and the residual component of the waveform have been examined . Until a consensus is developed, criteria should be clearly defined and consistently used.
Although progress is being made in the computer-based interpretation of FHR records, with few exceptions, clinical records are read visually. The limited inter-observer reliability for the interpretation of FHR variables has been well documented . Our experience has demonstrated the following good-to-fair inter-observer Kappa values: baseline FHR, 0.70; baseline FHR variability, 0.55; FHR accelerations, 0.57; variable decelerations, 0.46 and late and prolonged decelerations, 0.57. Scoring FHR patterns over time can offset this limited inter-observer reliability of individual FHR variables. The record should be scored in 10 min epochs (cycles). Determination of the pattern requires careful scoring of a number of cycles that in most cases can be achieved with six cycles representing 1 h of the FHR record. Our experience has been a high degree of inter-observer reliability in the classification of FHR patterns in 1 h of recording .
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