Guidelines on fetal monitoring aim to codify normal, abnormal FHR
Any fetal heart rate pattern will now reside in 1 of 3 categories. Will this improve the way you manage labor? How?
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.
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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.
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.
1. Macones GA, Hankins GDV, Spong CY, Hauth J, Moore T. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines. Obstet Gynecol. 2008;112:661-666.
2. US Preventive Services Task Force. Screening for intrapartum electronic fetal monitoring, topic page. Rockville, MD: Agency for Healthcare Research and Quality; 1996. http://www.ahrq.gov/clinic/uspstf/uspsiefm.htm. Accessed September 16, 2008.
3. Anderson G. Intrapartum electronic fetal monitoring. In: Canadian Task Force on the Periodic Health Examination. Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada; 1994:158–165.
4. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin. Clinical Management Guidelines for Obstetrician-Gynecologists, Number 70, December 2005 (Replaces Practice Bulletin Number 62, May 2005). Intrapartum fetal heart rate monitoring. Obstet Gynecol. 2005;106:1453-1460.
5. Skupski DW, Rosenberg CR, Eglinton GS. Intrapartum fetal stimulation tests: a meta-analysis. Obstet Gynecol. 2002;99:129-134.
6. Blix E, Sviggum O, Koss KS, Øian P. Inter-observer variation in assessment of 845 labour admission tests: comparisons between midwives and obstetricians in the clinical setting and two experts. BJOG. 2003;110:1-5.