To improve communication among nurses and physicians, it helps for each labor unit to accept a uniform approach to how FHR tracings are interpreted. Focusing on FHR variability and accurate identification of late and variable decelerations is of particular importance (see “2 keys to interpreting FHR tracings,”).
2 KEYS TO INTERPRETING FHR TRACINGS
- Focus on assessment of variability
- Accurately identify type of deceleration
Fetal heart rate variability
Assessment of variability is an important part of interpreting a fetal heart rate (FHR) pattern. Baseline FHR is defined as fluctuations in the baseline of irregular amplitude and frequency. These fluctuations are quantified in terms of the amplitude of the peak-to-trough in beats per minute (bpm). Baseline FHR variability is determined on a 10-minute segment of the FHR strip.
FHR variability is assigned to one of four possible categories:
- Absent. No peak-to-trough changes in FHR detected
- Minimal. Amplitude is >0 and ≤5 bpm
- Moderate. Amplitude is 6–25 bpm
- Marked. Amplitude is >25 bpm.
The presence of moderate variability is strongly predictive of normal fetal acid–base status. Absent variability is an ominous finding, especially when it occurs in conjunction with late or variable declerations.
Differentiating the 3 types of deceleration
When reviewing FHR tracings, clinicians often disagree on the identification of various types of FHR decelerations. The NICHD guidelines provide clear advice on interpreting deceleration patterns.
A variable deceleration is an abrupt decrease in FHR. If the time from baseline to the nadir of the deceleration is 30 seconds or longer, the deceleration cannot be considered variable; it must be either an early or a late deceleration.
A late deceleration has a nadir that occurs after the peak of the contraction.
An early deceleration has a nadir that occurs at the same time as the peak of the contraction.
A clearly documented contraction pattern is necessary to accurately differentiate late and early decelerations.
This tool offers welcome uniformity
For practical reasons, obstetricians in the United States have accepted FHR monitoring as a standard component of labor management. Given that we have accepted this technology, we can improve the consistency of our approach to interpreting FHR patterns by adopting a uniform set of definitions of what is normal and what is abnormal. Focusing on FHR variability and correctly identifying the type of deceleration that is present are the two best ways to achieve a unified approach to using FHR patterns to guide management of labor.