Dozens of times, every week, obstetricians are guided by the results of electronic fetal heart rate (FHR) monitoring when they make labor management decisions. Now, The National Institute of Child Health and Human Development (NICHD), along with ACOG and the Society for Maternal–Fetal Medicine, have revisited the nomenclature for interpreting FHR patterns.1 I’ll explain how the changes may affect your management of labor.
Does FHR monitoring have clinical value?
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FHR is, of course, a proxy for fetal acid–base status, oxygenation, and blood volume. Despite some modest scientific evidence that electronic FHR monitoring improves the outcome of labor for mother or newborn (compared with outcomes with intermittent auscultation), that conclusion is not what most studies reach; instead, in low-risk pregnancies, electronic FHR monitoring does not decrease the rate of perinatal complications and death, compared with intermittent auscultation, and does increase the rate of cesarean delivery.
The US Preventive Services Task Force2 and the Canadian Task Force on Preventive Health Care3 therefore recommend against routine electronic FHR monitoring for low-risk women in labor. Furthermore, both task forces have concluded that evidence is insufficient to recommend for, or against, electronic FHR monitoring in high-risk women in labor.
In contrast, a 2005 ACOG bulletin recommends continuous FHR monitoring for high-risk women during labor and intermittent FHR monitoring, by auscultation or electronic means, during labor in uncomplicated pregnancies.4 The bulletin notes that it may be logistically difficult on most labor units to adequately execute a plan to provide intermittent auscultation because the team does not have time to assess FHR frequently by auscultation.
From a practical viewpoint, medicolegal precedent and the opinion of OB experts has led to FHR monitoring of most laboring women in US hospitals.
“Normal,” “abnormal,” and “indeterminate” categories
New NICHD guidelines1 divide all FHR patterns into three categories:
Category I: Normal A Category I FHR pattern has the following four characteristics:
- baseline rate, 110–160 bpm
- moderate variability (6–25 bpm)
- absence of late or variable decelerations
- absence or presence of early decelerations or accelerations.
Patterns in Category I are almost always associated with normal fetal acid–base status. No specific obstetric intervention is necessary when a Category I FHR pattern is observed.
Category II: Indeterminate Category II comprises all FHR patterns not in Category I or III. Category II tracings are not predictive of abnormal fetal acid–base status. When a Category II tracing is identified, a fetal scalp stimulation test may help identify fetuses in which acid–base status is normal.
Category III: Abnormal The new NICHD guidelines label four FHR patterns as abnormal. One of the abnormal patterns is a sinusoidal heart rate, defined as a pattern of regular variability resembling a sine wave, with fixed periodicity of 3–5 cycles/ min and amplitude of 5–40 bpm. A sinusoidal pattern may indicate fetal anemia caused by fetomaternal hemorrhage or alloimmunization.
The other three abnormal FHR patterns in Category III are diagnosed when baseline FHR variability is absent and any one of the following is present:
- recurrent late decelerations
- recurrent variable deceleration
These patterns are predictive of abnormal fetal acid–base status.
NICHD categories and practical matters
Management of labor is complex. When a Category I tracing is observed, obstetric issues, independent of the FHR tracing, occupy center stage in management.
When a Category II FHR tracing is observed, a fetal scalp stimulation test may help define fetal acid–base status. When gentle stroking of the fetal scalp for 15 seconds during a vaginal examination elicits an acceleration of 15 bpm for 15 seconds, fetal acid–base status is very likely normal.5
(Note: Fetal scalp stimulation is a diagnostic test, not a therapeutic intervention. The test should not be performed during a deceleration because the information gained in that setting doesn’t predict the acid–base status of the fetus.)
When a Category III tracing is observed, the presence of a responsible clinician at the bedside—one who is authorized to make decisions regarding timing and route of delivery—is of paramount importance. Efforts should be made to identify the cause of the nonreassuring FHR pattern and initiate a plan to improve fetal status. Standard interventions that may help to resolve the abnormal pattern (and that may also be warranted for some Category II tracings) include:
- supplemental oxygen to the mother
- a change in maternal position
- discontinuation of oxytocin
- resolution of maternal hypotension.
In most situations, expeditious delivery is likely warranted if an abnormal pattern persists.
Neutralizing a critical inconsistency—the observer
A major problem in the use of FHR tracings is significant interclinician variability in how they are interpreted.6 When clinicians disagree on the interpretation of a particular FHR pattern, it often becomes difficult to develop and execute a unified plan for managing the mother’s labor.