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Fetal Heart Rate Monitoring: The Good, the Bad, and the Atypical
Ashmead GG
The Female Patient. 2011;36(4):14-22

Intrapartum fetal heart rate monitoring is the most common obstetric procedure performed in the United States.

In 2002, 85% of the approximately 4 million live births in the United States were evaluated with electronic fetal monitoring (EFM). Fetal heart rate (FHR) is controlled by a balance between the fetal sympathetic and parasympathetic nervous system, and EFM is used by clinicians to assess fetal oxygenation.1

Despite the widespread use of EFM, there has been no decrease in cerebral palsy. Although intrapartum EFM abnormalities correlate with umbilical cord base excess and neonatal seizures, a metaanalysis of randomized control trials has shown that EFM has no eff ect in perinatal mortality or pediatric neurologic morbidity.2 However, EFM is associated with an increase in the rate of operative vaginal and cesarean deliveries.1

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CONFLICTING INTERPRETATION

There is considerable inter and intra variability in the interpretation of EFM. Clinicians disagree with each other in their evaluation of FHR about 80% of the time. Even when reviewing the same FHR pattern several months later, a clinician disagrees with his or her own initial interpretation about 20% of the time.1

One study by Chauhan et al had 5 clinicians evaluate the FHR patterns of 100 parturients using the traditional intrapartum evaluation (reassuring vs nonreassuring). Forty-six percent of these patients had an emergent cesarean delivery, and 2% had a fetal pH less than 7.0. Th e study found that not only was there poor agreement among clinicians, but they could not even predict which parturients had an emergent cesarean delivery or low fetal pH.3 Fetal metabolic acidosis and hypoxic-ischemic encephalopathy are also associated with signifi cant increases in EFM abnormalities, but EFM predictive ability to identify these conditions is low.4

Although intermittent fetal auscultation may be a theoretical option in low-risk patients, nursing staffi ng limitations make this impractical in a busy labor and delivery suite. Finally, regardless of the medical merits of intrapartum FHR monitoring, intermittent or continuous, auscultation or electronic, there is a medicolegal expectation in the United States of some form of fetal monitoring in labor.

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DEFINING CHARACTERISTICS

In 2008, the National Institute of Child Health and Human Development (NICHD) Workshop Report on EFM set forth recommendations for defining FHR characteristics to improve predictive value of EFM and facilitate evidencebased clinical management of fetal compromise. The NICHD defi nitions were created for visual interpretation of FHR patterns, with the understanding that the defi nitions should be adaptable to future computer interpretation.5,6 The FHR definitions are intended for evaluation of intrapartum patterns but may be used antepartum. A 3-Tier FHR Interpretation System was developed, defining a category I FHR tracing as normal, category III as abnormal, and the remaining category II as atypical or indeterminate.5 The 3 categories could be considered respectively: "good," "bad," and "atypical."

While there can be controversy about the need for yet another system to evaluate FHR patterns, defining some FHR patterns as clearly good or normal (category I) and some as clearly bad or abnormal (category III) is a step forward. Th e remaining atypical or indeterminate FHR patterns (category II) will always be with us and able to generate debate. See Table 1 (FHR defi nitions) and Table 2 (category definitions). Figures 1, 2, 3A, and 3B demonstrate samples of category I, II, and III FHR patterns.

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EVALUATION BASED ON CATEGORY

How should the current classifi cation of FHR categories be used? Category I, or good, FHR patterns are normal and require no specifi c action. Category I FHR patterns should reassure both patients and their clinicians. Category II, or indeterminant, FHR patterns are not predictive of abnormal fetal acid-base status and require evaluation in terms of overall clinical condition, reevaluation, and continued surveillance.1,5,7

Category III, or bad, FHR patterns are predictive of abnormal fetal acid-base status at the time of observation. Category III FHR tracings that require immediate action include an absent baseline FHR variability with recurrent late or variable decelerations, bradycardia, or a sinusoidal pattern.7 If possible, the cause of the nonreassuring FHR should be addressed. Th ese can include poor fetal oxygenation, uteroplacental perfusion, or umbilical cord compression. Some interventions include:

• Maternal oxygenation (100% O2 10 L/min nonrebreather face mask)
• Change in maternal position (right or left lateral positioning)
• If prolapsed umbilical cord is noted, elevate the presenting fetal part while preparations are made for operative delivery
• Discontinuation of labor stimulation (stopping uterotonic agents)
• Tocolytic therapy for tachysystole (eg, terbutaline)
• Treatment of maternal hypotension
• Intravenous fluid boluses (1,000 mL).1,5,7,8 If the Category III patterns persist and acidosis cannot be excluded, then appropriate management is expeditious delivery.

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CONCLUSION

Future research should be directed towards the category II indeterminate or atypical patterns and their relationship to clinical outcome. Computer analysis of FHR tracings may eventually further simplify and improve intrapartum care and management. In any case, the current classifi cation and suggested management of FHR tracings will hopefully result in a more beautiful future—avoiding both fetal acidosis and unnecessary intervention, while improving patient care.

ACKNOWLEDGMENT

The author wishes to thank Anne Lucas, MSN, RNC, Winthrop University Hospital, for the images of fetal heart rate tracings.

The author reports no actual or potential confl ict of interest in relation to this article.

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Graham Gaylord Ashmead, MD, FACOG, is Maternal- Fetal Medicine Subspecialist, Department of ObGyn, St. Luke's-Roosevelt Hospital, New York, NY.

References

 

  1. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 106: Intrapartum fetal heart rate monitoring: nomenclature, interpretation, and general management principles. Obstet Gynecol. 2009;114(1):192-202.
  2. Graham EM, Peterson SM, Christo DK, Fox HE. Intrapartum electronic fetal heart rate monitoring and the prevention of perinatal brain injury. Obstet Gynecol. 2006;108(3 Pt 1):656-666.
  3. Chauhan SP, Klauser CK, Woodring TC, Sanderson M, Magann EF, Morrison JC. Intrapartum nonreassuring fetal heart rate tracing and prediction of adverse outcomes: interobserver variability. Am J Obstet Gynecol. 2008;199(6):623.e1-e5.
  4. Larma JD, Silva AM, Holcroft CJ, Thompson RE, Donohue PK, Graham EM. Intrapartum electronic fetal heart rate monitoring and the identification of metabolic acidosis and hypoxic-ischemic encephalopathy. Am J Obstet Gynecol. 2007;197(3):301.e1-e8.
  5. Macones GA, Hankins GD, 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(3):661-666.
  6. Costa A, Ayres-de-Campos D, Costa F, Santos C, Bernardes J. Prediction of neonatal acidemia by computer analysis of fetal heart rate and ST event signals. Am J Obstet Gynecol. 2009;201(5):464.e1-e6.
  7. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 116: Management of intrapartum fetal heart rate tracings. Obstet Gynecol. 2010;116(5):1232-1240.
  8. Simpson KR, James DC. Efficacy of intrauterine resuscitation techniques in improving fetal oxygen status during labor. Obstet Gynecol. 2005;105(6): 1362-1368.

 


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