Current Commentary

The 2008 National Institute of Child Healthand Human Development Workshop Reporton Electronic Fetal MonitoringUpdate on Definitions, Interpretation, and Research Guidelines

George A. Macones, MD, Gary D. V. Hankins, MD, Catherine Y. Spong, MD, John Hauth, MD,and Thomas Moore, MD

In April 2008, the Eunice KennedyShriver National Institute of ChildHealth and Human Development, theAmerican College of Obstetricians

and Gynecologists, and the Societyfor Maternal-Fetal Medicine part-nered to sponsor a 2-day workshopto revisit nomenclature, interpreta-tion, and research recommendationsfor intrapartum electronic fetal heartrate monitoring. Participants includedobstetric experts and representativesfrom relevant stakeholder groups andorganizations. This article provides asummary of the discussions at theworkshop. This includes a discussionof terminology and nomenclature forthe description of fetal heart tracingsand uterine contractions for use inclinical practice and research. Athree-tier system for fetal heart ratetracing interpretation is also de-scribed. Lastly, prioritized topics forfuture research are provided.(Obstet Gynecol 2008;112:661–6)

The Eunice Kennedy Shriver Na-tional Institute of Child Health

and Human Development (NICHD)convened a series of workshops inthe mid- 1990s to develop standard-ized and unambiguous definitionsfor fetal heart rate (FHR) tracings,culminating in a publication of rec-ommendations for defining fetalheart rate characteristics.1 The goalof these definitions was to allow thepredictive value of monitoring tobe assessed more meaningfully andto allow evidence-based clinical

management of intrapartum fetalcompromise.

The definitions agreed upon inthat workshop were endorsed forclinical use in the most recent Amer-ican College of Obstetricians andGynecologists (ACOG) Practice Bul-letin in 2005 and also endorsed bythe Association of Women’s Health,Obstetric and Neonatal Nurses.2

Subsequently, the Royal College ofObstetricians and Gynaecologists(RCOG, 2001) and the Society ofObstetricians and Gynaecologists ofCanada (SOGC, 2007) convened ex-pert groups to assess the evidence-based use of electronic fetal monitor-ing (EFM). These groups producedconsensus documents with morespecific recommendations for FHRpattern classification and intrapar-tum management actions.3,4 In addi-tion, new interpretations and defini-tions have been proposed, includ-ing terminology such as “tachysys-tole” and “hyperstimulation” andnew interpretative systems usingthree and five tiers.3–5 The SOGCConsensus Guidelines for FetalHealth Surveillance presents athree-tier system (normal, atypical,abnormal), as does RCOG.3,4 Parerand Ikeda5 recently suggested afive-tier management grading sys-tem. Recently, the NICHD, ACOG,and the Society for Maternal-Fetal

See related editorial on page 506.

From the Department of Obstetrics and Gynecology,Washington University in St. Louis, St. Louis,Missouri; Department of Obstetrics and Gynecology,University of Texas Medical Branch, Galveston,Texas; Eunice Kennedy Shriver National Institute ofChild Health and Human Development, Bethesda,Maryland; Department of Obstetrics and Gynecol-ogy, University of Alabama at Birmingham, Bir-mingham, Alabama; and Department of Obstetricsand Gynecology, University of California at SanDiego, San Diego, California.

For a list of workshop participants, see the Appendixonline at www.greenjournal.org/cgi/content/full/112/3/661/DC1.

The workshop was jointly sponsored by the AmericanCollege of Obstetricians and Gynecologists, the Eu-nice Kennedy Shriver National Institute of ChildHealth and Human Development, and the Society forMaternal-Fetal Medicine.

The recommendations from the National Institute ofChild Health and Human Development 2008Workshop are being published simultaneously byObstetrics & Gynecology and the Journal ofObstetric, Gynecologic, & Neonatal Nursing.

Corresponding author: George A. Macones, MD,Chair, Department of Obstetrics and Gynecology,Washington University in St Louis, MI 63110;e-mail: maconesg@wustl.edu.

Financial DisclosureThe authors have no potential conflicts of interest todisclose.

© 2008 by The American College of Obstetriciansand Gynecologists. Published by Lippincott Williams& Wilkins.ISSN: 0029-7844/08

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Medicine jointly sponsored a work-shop focused on EFM. The goals ofthis workshop were 1) to review andupdate the definitions for FHR pat-tern categorization from the priorworkshop; 2) to assess existing clas-sification systems for interpretingspecific FHR patterns and to makerecommendations about a system foruse in the United States; and 3) tomake recommendations for researchpriorities for EFM. Thus, while goals1 and 3 are similar to the priorworkshop, a new emphasis on inter-pretative systems (goal 2) was part ofthe recent workshop.

As was true in the prior publica-tion,1 before presenting actual defini-tions and interpretation, it is neces-sary to state a number of assumptionsand factors common to FHR inter-pretation in the United States.These were defined in the initialpublication1 and were affirmedand/or updated by the panel:

A. The definitions are primarilydeveloped for visual interpreta-tion of FHR patterns. However,it is recognized that computer-ized interpretation is being de-veloped and the definitionsmust also be adaptable to suchapplications.

B. The definitions apply to the in-terpretations of patterns pro-duced from either a direct fetalelectrode detecting the fetalelectrocardiogram or an exter-nal Doppler device detectingthe fetal heart rate events withuse of the autocorrelation tech-nique.

C. The record of both the FHRand uterine activity should beof adequate quality for visualinterpretation.

D. The prime emphasis in this re-port is on intrapartum patterns.The definitions may also be ap-plicable to antepartum observa-tions.

E. The characteristics to be de-fined are those commonly usedin clinical practice and researchcommunications.

F. The features of FHR patternsare categorized as either base-line, periodic, or episodic. Peri-odic patterns are those associ-ated with uterine contractions,and episodic patterns are thosenot associated with uterine con-tractions.

G. The periodic patterns are distin-guished on the basis of wave-form, currently accepted as ei-ther “abrupt” or “gradual” onset.

H. Accelerations and decelera-tions are generally determinedin reference to the adjacentbaseline FHR.

I. No distinction is made betweenshort-term variability (or beat-to-beat variability or R–R waveperiod differences in the elec-trocardiogram) and long-termvariability, because in actualpractice they are visually deter-mined as a unit. Hence, thedefinition of variability is basedvisually on the amplitude of thecomplexes, with exclusion ofthe sinusoidal pattern.

J. There is good evidence that anumber of characteristics ofFHR patterns are dependentupon fetal gestational age andphysiologic status as well as ma-ternal physiologic status. Thus,FHR tracings should be evalu-ated in the context of manyclinical conditions includinggestational age, prior results offetal assessment, medications,maternal medical conditions,and fetal conditions (eg, growthrestriction, known congenitalanomalies, fetal anemia, ar-rhythmia, etc).

K. The individual components ofdefined FHR patterns do notoccur independently and gen-erally evolve over time.

L. A full description of an EFMtracing requires a qualitativeand quantitative description of:1. Uterine contractions.2. Baseline fetal heart rate.3. Baseline FHR variability.4. Presence of accelerations.5. Periodic or episodic deceler-

ations.6. Changes or trends of FHR

patterns over time.

Uterine contractions are quanti-fied as the number of contractionspresent in a 10-minute window,averaged over 30 minutes. Con-traction frequency alone is a partialassessment of uterine activity.Other factors such as duration, in-tensity, and relaxation time be-tween contractions are equally im-portant in clinical practice.

The following represents termi-nology to describe uterine activity:

A. Normal: �5 contractions in 10minutes, averaged over a 30-minute window.

B. Tachysystole: �5 contractions in10 minutes, averaged over a30-minute window.

C. Characteristics of uterine contractions:• Tachysystole should always

be qualified as to the pres-ence or absence of associatedFHR decelerations.

• The term tachysystole ap-plies to both spontaneous orstimulated labor. The clinicalresponse to tachysystole maydiffer depending on whethercontractions are spontaneousor stimulated.

• The terms hyperstimulationand hypercontractility arenot defined and should beabandoned.

Fetal heart rate patterns are de-fined by the characteristics of base-line, variability, accelerations, anddecelerations.

The baseline FHR is determinedby approximating the mean FHR

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rounded to increments of 5 beatsper minute (bpm) during a 10-minute window, excluding acceler-ations and decelerations and peri-ods of marked FHR variability(�25 bpm). There must be at least2 minutes of identifiable baselinesegments (not necessarily contigu-ous) in any 10-minute window, orthe baseline for that period is inde-terminate. In such cases, it may benecessary to refer to the previous10-minute window for determina-tion of the baseline. Abnormalbaseline is termed bradycardia whenthe baseline FHR is �110 bpm; it istermed tachycardia when the base-line FHR is �160 bpm.

Baseline FHR variability is deter-mined in a 10-minute window, ex-cluding accelerations and decelera-tions. Baseline FHR variability isdefined as fluctuations in the base-line FHR that are irregular in ampli-tude and frequency. The fluctuationsare visually quantitated as the ampli-tude of the peak-to-trough in bpm.

Variability is classified as fol-lows: Absent FHR variability: am-plitude range undetectable. Mini-mal FHR variability: amplituderange�undetectable and �5 bpm.Moderate FHR variability: amplituderange 6 bpm to 25 bpm. MarkedFHR variability: amplitude range�25 bpm.

An acceleration is a visually ap-parent abrupt increase in FHR. Anabrupt increase is defined as anincrease from the onset of acceler-ation to the peak in �30 seconds.To be called an acceleration, thepeak must be �15 bpm, and theacceleration must last �15 secondsfrom the onset to return. A pro-longed acceleration is �2 minutesbut �10 minutes in duration. Fi-nally, an acceleration lasting �10minutes is defined as a baselinechange. Before 32 weeks of gesta-tion, accelerations are defined ashaving a peak �10 bpm and aduration of �10 seconds.

Decelerations are classified aslate, early, or variable based onspecific characteristics (see the Box,“Characteristics of Decelerations”).Variable decelerations may be ac-companied by other characteris-tics, the clinical significance ofwhich requires further research in-vestigation. Some examples in-clude a slow return of the FHR afterthe end of the contraction, biphasicdecelerations, tachycardia after vari-able deceleration(s), accelerationspreceding and/or following, some-times called “shoulders” or “over-shoots,” and fluctuations in the FHRin the trough of the deceleration.

A prolonged deceleration ispresent when there is a visuallyapparent decrease in FHR from thebaseline that is �15 bpm, lasting�2 minutes, but �10 minutes. Adeceleration that lasts �10 minutesis a baseline change.

A sinusoidal fetal heart rate patternis a specific fetal heart rate patternthat is defined as having a visuallyapparent, smooth, sine wave–likeundulating pattern in FHR baselinewith a cycle frequency of 3–5/minthat persists for �20 minutes.

Quantitation of DecelerationsThe magnitude of a deceleration isquantitated by the depth of the nadirin beats per minute (excluding tran-sient spikes or electronic artifact).The duration is quantitated in min-utes and seconds from the beginningto the end of the deceleration. Accel-erations are quantitated similarly.

Some authors have suggestedgrading of decelerations based onthe depth of the deceleration orabsolute nadir in beats per minuteand duration.4–7 These grading sys-tems require further investigationas to their predictive value.

Decelerations are defined as re-current if they occur with �50% ofuterine contractions in any 20-minute window. Decelerations oc-

curring with �50% of uterine con-tractions in any 20-minute segmentare defined as intermittent.

General Considerations forthe Interpretation of FetalHeart Rate PatternsA variety of systems for EFMinterpretation have been devel-oped and propagated in theUnited States and worldwide.3–5

Any interpretation system mustbe based, to the greatest extentpossible, on existing evidence(recognizing that in some areasevidence is lacking). In addition,any system should be simple andapplicable to clinical practice.

Given that the fetal heart rateresponse is a dynamic process, andone that evolves over time, thecategories of FHR patterns are dy-namic and transient, requiring fre-quent reassessment. It is commonfor FHR tracings to move from onecategory to another over time.

The FHR tracing should be in-terpreted in the context of the over-all clinical circumstances, and cate-gorization of a FHR tracing islimited to the time period beingassessed. The presence of FHR ac-celerations (either spontaneous orstimulated) reliably predicts the ab-sence of fetal metabolic acidemia.The absence of accelerations doesnot, however, reliably predict fetalacidemia. Fetal heart rate accelera-tions can be stimulated with a vari-ety of methods (vibroacoustic,transabdominal halogen light, anddirect fetal scalp stimulation).

Moderate FHR variability reli-ably predicts the absence of fetalmetabolic acidemia at the time it isobserved. Minimal or absent FHRvariability alone does not reliablypredict the presence of fetal hypox-emia or metabolic acidemia. Thesignificance of marked FHR (previ-ously described as saltatory) vari-ability is unclear.

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Interpretation of Fetal HeartRate PatternsBased on careful review of theavailable options, a three-tier sys-tem for the categorization of FHRpatterns is recommended (see theBox, “Three-Tier Fetal Heart RateInterpretation System”). Althoughthe development of managementalgorithms is a function of profes-sional specialty entities, some gen-eral management principles wereagreed upon for these categories.Fetal heart rate tracing patternsprovide information on the currentacid–base status of the fetus andcannot predict the development ofcerebral palsy. Categorization ofthe FHR tracing evaluates the fetusat that point in time; tracing pat-terns can and will change. A FHR

tracing may move back and forthbetween categories depending onthe clinical situation and manage-ment strategies employed.

Category I FHR tracings arenormal. Category I FHR tracingsare strongly predictive of normalfetal acid– base status at the timeof observation. Category I FHRtracings may be followed in aroutine manner, and no specificaction is required.

Category II FHR tracings are in-determinate. Category II FHR trac-ings are not predictive of abnormalfetal acid–base status, yet we do nothave adequate evidence at present toclassify these as Category I or Cate-gory III. Category II FHR tracingsrequire evaluation and continuedsurveillance and reevaluation, taking

into account the entire associatedclinical circumstances.

Category III FHR tracings areabnormal. Category III tracings arepredictive of abnormal fetal acid–base status at the time of observa-tion. Category III FHR tracingsrequire prompt evaluation. De-pending on the clinical situation,efforts to expeditiously resolve theabnormal FHR pattern may include,but are not limited to, provision ofmaternal oxygen, change in mater-nal position, discontinuation of la-bor stimulation, and treatment ofmaternal hypotension.

Research RecommendationsSince the last workshop, there hasnot been a wealth of research onEFM. With the high penetrance of

Characteristics of Decelerations

Late Deceleration

• Visually apparent usually symmetrical gradual decrease and return of the fetal heart rate (FHR)associated with a uterine contraction.

• A gradual FHR decrease is defined as from the onset to the FHR nadir of �30 seconds.• The decrease in FHR is calculated from the onset to the nadir of the deceleration.• The deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of

the contraction.• In most cases, the onset, nadir, and recovery of the deceleration occur after the beginning, peak, and

ending of the contraction, respectively.

Early Deceleration

• Visually apparent, usually symmetrical, gradual decrease and return of the FHR associated witha uterine contraction.

• A gradual FHR decrease is defined as one from the onset to the FHR nadir of �30 seconds.• The decrease in FHR is calculated from the onset to the nadir of the deceleration.• The nadir of the deceleration occurs at the same time as the peak of the contraction.• In most cases the onset, nadir, and recovery of the deceleration are coincident with the beginning,

peak, and ending of the contraction, respectively.

Variable Deceleration

• Visually apparent abrupt decrease in FHR.• An abrupt FHR decrease is defined as from the onset of the deceleration to the beginning of the FHR nadir

of �30 seconds. The decrease in FHR is calculated from the onset to the nadir of the deceleration.• The decrease in FHR is �15 beats per minute, lasting �15 seconds, and �2 minutes in duration.• When variable decelerations are associated with uterine contractions, their onset, depth, and duration commonly

vary with successive uterine contractions.

664 Macones et al Electronic Fetal Heart Rate Monitoring OBSTETRICS & GYNECOLOGY

this technology into obstetric prac-tice, well-designed studies areneeded to fill gaps in knowledge.Areas of highest priority for re-search include observational stud-ies focused on indeterminate FHRpatterns, including descriptive epi-demiology, frequency of specificpatterns, change over time, the re-

lationship to clinically relevant out-comes, and the effect of duration ofpatterns (eg, recurrent late deceler-ations with minimal variability) onclinical outcomes. Other neededstudies include work that evaluatescontraction frequency, strength,and duration on FHR and clinicaloutcomes. Research also needs to

be focused on the effectiveness ofeducational programs on EFM thatinclude all relevant stakeholders.Although computerized interpreta-tion systems have not developed asrapidly as anticipated, studies areneeded on the effectiveness of com-puterized compared with providerinterpretation, including the analy-

Three-Tier Fetal Heart Rate Interpretation System

Category I

Category I fetal heart rate (FHR) tracings include all of the following:

• Baseline rate: 110–160 beats per minute (bpm)• Baseline FHR variability: moderate• Late or variable decelerations: absent• Early decelerations: present or absent• Accelerations: present or absent

Category II

Category II FHR tracings include all FHR tracings not categorized as Category I or Category III. Category IItracings may represent an appreciable fraction of those encountered in clinical care. Examples of Category IIFHR tracings include any of the following:

Baseline rate

• Bradycardia not accompanied by absent baseline variability• Tachycardia

Baseline FHR variability• Minimal baseline variability• Absent baseline variability not accompanied by recurrent decelerations• Marked baseline variability

Accelerations• Absence of induced accelerations after fetal stimulation

Periodic or episodic decelerations• Recurrent variable decelerations accompanied by minimal or moderate baseline variability• Prolonged deceleration �2 minutes but �10 minutes• Recurrent late decelerations with moderate baseline variability• Variable decelerations with other characteristics, such as slow return to baseline, “overshoots,”

or “shoulders”

Category III

Category III FHR tracings include either:

• Absent baseline FHR variability and any of the following:- Recurrent late decelerations- Recurrent variable decelerations- Bradycardia

• Sinusoidal pattern

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sis of existing data sets. Other areasfor work include the developmentof new comprehensive data setsintegrating outcomes with EFM indigitally addressable format and re-search on effectiveness of tech-niques supplementary to EFM,such as ST segment analysis.

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