FHR Monitoring: Nomenclature and Algorithms

Educational Objectives

The goal of this program is to improve identification and management of category II fetal heart rate tracings. After hearing and assimilating this program, the clinician will be better able to:

1. Interpret fetal heart rate tracings according to the 3-tiered system published by the National Institutes of Health and the 5-tiered system proposed by Parer et al. 
2. Discuss the findings of studies that assessed correlations of parameters in cord blood gases with neonatal outcomes. 

Summary

Consensus conference: National Institutes of Health consensus conference created 3-tiered system for analyzing fetal heart rate tracings (FHTs); category III tracing — concerning findings include absence of variability in combination with recurrent late or variable decelerations or bradycardia; category II tracing — requires continued surveillance (for unspecified time); findings may include bradycardia, tachycardia, minimal or marked variability, absent variability without decelerations, absence of accelerations after fetal stimulation, recurrent variable decelerations with minimal or moderate variability, prolonged decelerations, recurrent late decelerations with moderate variability, and variable decelerations with concerning characteristics with moderate variability

Issues with monitoring: clinician cannot wait for confirmation of acidosis before taking action; categories created based on risk for fetal metabolic acidosis; however, abnormal FHR patterns, interventions, and outcomes have not been studied in prospective blinded fashion; likelihood and rapidity of progression of FHR pattern from category II to category III unknown; fetal monitoring is not diagnostic test and characterized by high rate of false positives and poor specificity; positive predictive value of normal test high; FHT must be interpreted in context of parity and stage of labor

Clinical correlates of acidosis: in case-control study, Low et al evaluated thresholds in cord blood gases (CBG); found only base deficit (BD) >12 mEq/L associated with moderate or severe encephalopathy and respiratory complications; incidence of moderate or severe encephalopathy 10% when BD 12 to 16 mEq/L, 40% when BD >16 mEq/L, and 2% when BD <12 mEq/L; BD low in only 2% of term newborns

Patterns of FHR: >40 combinations of patterns possible on category II FHT, suggesting that current method for interpreting FHTs oversimplified; categorization ignores fact that even in absence of variability, hypoxia unlikely in fetus without late or variable decelerations; hypoxia, infection, drugs, and neurologic deficits affect variability; in animal models of hypoxia, confirmed in humans, decelerations always preceded loss of variability when poor variability related to hypoxia; isolated evolving patterns such as tachycardia and minimal variability without decelerations unlikely to be associated with acidosis

Problems with category II: category lumps patterns unlikely to be associated with hypoxia together with more concerning findings, relies heavily on variability, ignores data from fetal pulse oximetry studies, and ignores progression and duration of decelerations and combinations of findings; American College of Obstetricians and Gynecologists (ACOG) does not recommend specific interventions

Reliance on variability: according to proposed algorithm, variability must be absent or minimal to warrant intervention in patient with category II FHT; however, minimal or absent variability does not confirm acidosis; variability affected by sleep cycle, previous injury to brain, anomalies, genetic disorders, brain tumor, trauma, and toxins; conversely, metabolic acidosis or neurologic damage may occur in fetus with adequate variability

Case: patient presented at term with painful contractions and ≈150 mL of bright red vaginal bleeding; FHT showed variability and accelerations; best method for management of abruption depends on progress in labor and parity; patient developed late decelerations and delivered 2700-g infant; Apgar scores 3, 7, and 7 but CBG abnormal; newborn diagnosed with neonatal encephalopathy and possible hypoxic ischemic encephalopathy

Assessing variability: 3-tiered system relies heavily on variability; study evaluated assessments of 150 FHTs by 3 maternal-fetal medicine specialists; agreement on heart rate parameters poor across evaluators (κ=0.81 to 0.16); lowest concordance associated with assessment of absent variability; in another study, 5 clinicians reviewed 100 FHTs; concordance poor with respect to assessment of variability (κ=0 to 0.19) and tachycardia

Correlation of FHT with CBG: Ross et al assessed BD, lactate, variable decelerations, and cord compression in sheep; accumulation of BD correlated with severity of variable decelerations (0.21 mEq/L/min for mild decelerations, 0.27 mEq/L/min for moderate decelerations, and higher for severe decelerations); in another study, among 36 infants with BD >12 mEq/L, variability decreased or absent in 15 and normal in 21; in similar study, among 57 infants with adverse outcomes and pH <7.1, 52 had moderate variability; these studies show that presence of variability not necessarily reassuring

Assessment of category II FHT: although several constellations of findings are classified as category II, they have different implications and require individualized management; infant with variability and no decelerations not concerning; however, clinician should be cautious in other scenarios; proposed management scheme does not consider severity, combinations of patterns, duration, stage of labor, or progression of patterns

Color-coded assessment: Parer et al suggested using variability (normal, minimal, or absent) to triage FHT; next, other characteristics of FHR examined (presence of tachycardia; mild, moderate, or severe decelerations); combinations of these characteristics then color-coded and associated with suggested approach; this approach only method with proven efficacy for managing category II FHTs; study that evaluated correlation of base excess with colors and outcomes found that degree and duration of abnormalities on FHT related to outcomes; another case-control study compared patients with cord pH <7 to those with pH >7.2 (24 patients in each group); most patients had category II FHT; patients in low-pH group more likely to have category III tracing at some time (79% vs 12%); authors deemed this 5-tiered system superior to 3-tiered system for identifying fetal metabolic acidemia

Algorithm: Clark et al developed algorithm and flowchart for management that accounts for significant decelerations, stage and progress of labor, and presence of accelerations; minimal and absent variability combined; method acknowledges that some clinical situations should be managed with lower threshold for intervention (eg, abruption and trial of labor after cesarean delivery)

Summary: using uniform management scheme for every category II pattern not consistent with current understanding of likelihood of hypoxia across this diverse group; management scheme recommended by ACOG for category II tracing does not account for number of clinical parameters; clinicians should consider using 5-tiered system for management of FHTs suggested by Parer et al

Suggested ReadingsAcknowledgments

Dr. Shaffer and Dr. Nageotte were recorded at the 42nd Annual Antepartum and Intrapartum Management, presented by the USCF Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco School of Medicine, and held June 7-9, 2018, in San Francisco, CA. For information on upcoming CME meetings presented by the University of California, San Francisco School of Medicine, please visit meded.ucsf.edu/continuing-education. The Audio Digest Foundation thanks the speakers and the University of California, San Francisco School of Medicine for their cooperation in the production of this program.

Readings

Blackwell SC et al: Interobserver and intraobserver reliability of the NICHD 3-Tier Fetal Heart Rate Interpretation System. Am J Obstet Gynecol 2011 Oct;205(4):378.e1-5; Clark SL et al: Intrapartum management of category II fetal heart rate tracings: towards standardization of care. Am J Obstet Gynecol 2013 Aug;209(2):89-97; Coletta J et al: The 5-tier system of assessing fetal heart rate tracings is superior to the 3-tier system in identifying fetal acidemia. Am J Obstet Gynecol 2012 Mar;206(3):226.e1-5; Elliott C et al: Graded classification of fetal heart rate tracings: association with neonatal metabolic acidosis and neurologic morbidity. Am J Obstet Gynecol 2010 Mar;202(3):258.e1-8; Katsuragi S et al: Mechanism of reduction of newborn metabolic acidemia following application of a rule-based 5-category color-coded fetal heart rate management framework. J Matern Fetal Neonatal Med 2015 Sep;28(13):1608-13; Low JA et al: Threshold of metabolic acidosis associated with newborn complications. Am J Obstet Gynecol 1997 Dec;177(6):1391-4; Ross MG et al: Correlation of arterial fetal base deficit and lactate changes with severity of variable heart rate decelerations in the near-term ovine fetus. Am J Obstet Gynecol 2013 Apr;208(4):285.e1-6; Williams KP, Galerneau F: Intrapartum fetal heart rate patterns in the prediction of neonatal acidemia. Am J Obstet Gynecol 2003 Mar;188(3):820-3.

Disclosures

For this program, members of the faculty and planning committee reported nothing to disclose.

Acknowledgements

Dr. Shaffer and Dr. Nageotte were recorded at the 42nd Annual Antepartum and Intrapartum Management, presented by the USCF Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco School of Medicine, and held June 7-9, 2018, in San Francisco, CA. For information on upcoming CME meetings presented by the University of California, San Francisco School of Medicine, please visit meded.ucsf.edu/continuing-education. The Audio Digest Foundation thanks the speakers and the University of California, San Francisco School of Medicine for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

OB660502

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.