Strip of the Month: October 2011Maurice L. Druzin, MD,*

Nancy Peterson, RNC,

PNNP, MSN, IBLC†

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Electronic Fetal Monitoring Case Review SeriesElectronic fetal monitoring (EFM) is a popular technology used to establish fetal well-being. Despite its widespread use, terminology used to describe patterns seen on themonitor has not been consistent until recently. In 1997, the National Institute of ChildHealth and Human Development (NICHD) Research Planning Workshop publishedguidelines for interpretation of fetal tracings. This publication was the culmination of 2years of work by a panel of experts in the field of fetal monitoring and was endorsed in 2005by both the American College of Obstetricians and Gynecologists (ACOG) and theAssociation of Women’s Health, Obstetric and Neonatal Nurses (AWHONN). In 2008,ACOG, NICHD, and the Society for Maternal-Fetal Medicine reviewed and updated thedefinitions for fetal heart rate patterns, interpretation ,and research recommendations.Following is a summary of the terminology definitions and assumptions found in the 2008NICHD workshop report. Normal values for arterial umbilical cord gas values andindications of acidosis are defined in Table 1.

Assumptions from the NICHD Workshop● Definitions are developed for visual interpretation, assuming that both the fetal heart rate

(FHR) and uterine activity recordings are of adequate quality● Definitions apply to tracings generated by internal or external monitoring devices● Periodic patterns are differentiated based on waveform, abrupt or gradual (eg, late

decelerations have a gradual onset and variable decelerations have an abrupt onset)● Long- and short-term variability are evaluated visually as a unit● Gestational age of the fetus is considered when evaluating patterns● Components of fetal heart rate FHR do not occur alone and generally evolve over time

DefinitionsBaseline Fetal Heart Rate

● Approximate mean FHR rounded to increments of 5 beats/min in a 10-minute segmentof tracing, excluding accelerations and decelerations, periods of marked variability, andsegments of baseline that differ by �25 beats/min

● In the 10-minute segment, the minimum baseline duration must be at least 2 minutes(not necessarily contiguous) or the baseline for that segment is indeterminate

● Bradycardia is a baseline of �110 beats/min; tachycardia is a baseline of�160 beats/min

● Sinusoidal baseline has a smooth sine wave-like undulating pattern, with waves havingregular frequency and amplitude

Baseline Variability

● Fluctuations in the baseline FHR of two cycles per minute or greater, fluctuations areirregular in amplitude and frequency, fluctuations are visually quantitated as the ampli-tude of the peak to trough in beats per minute

● Classification of variability:Absent: Amplitude range is undetectableMinimal: Amplitude range is greater than undetectable to 5 beats/minModerate: Amplitude range is 6 to 25 beats/minMarked: Amplitude range is �25 beats/min

*Charles B. and Ann L. Johnson Professor of Obstetrics; Chief, Division of Maternal-Fetal Medicine; Co-Medical Director, Mid-Coastal California Perinatal Outreach Program, Stanford University School of Medicine, Palo Alto, Calif.†Director of Perinatal Outreach, Stanford University, Palo Alto, Calif.

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Accelerations

● Abrupt increase in FHR above the most recently deter-mined baseline

● Onset to peak of acceleration is �30 seconds, acme is�15 beats/min above the most recently determinedbaseline and lasts �15 seconds but �2 minutes

● Before 32 weeks’ gestation, accelerations are definedby an acme �10 beats/min above the most recentlydetermined baseline for �10 seconds

● Prolonged acceleration lasts �2 minutes but �10 min-utes

Late Decelerations

● Gradual decrease in FHR (onset to nadir �30 seconds)below the most recently determined baseline, withnadir occurring after the peak of uterine contractions

● Considered a periodic pattern because it occurs withuterine contractions

Early Decelerations

● Gradual decrease in FHR (onset to nadir �30 seconds)below the most recently determined baseline, withnadir occurring coincident with uterine contraction

● Also considered a periodic pattern

Variable Decelerations

● Abrupt decrease in FHR (onset to nadir �30 seconds)● Decrease is �15 beats/min below the most recently

determined baseline lasting �15 seconds but �2 min-utes

● May be episodic (occurs without a contraction) orperiodic

Prolonged Decelerations

● Decrease in the FHR �15 beats/min below the mostrecently determined baseline lasting �2 minutes but�10 minutes from onset to return to baseline

Decelerations are tentatively called recurrent if they oc-cur with �50% of uterine contractions in a 20-minuteperiod.

Decelerations occurring with �50% of uterine contrac-tions in a 20-minute segment are intermittent.

Sinusoidal Fetal Heart Rate Pattern

● Visually apparent, smooth sine wavelike undulatingpattern in the baseline with a cycle frequency of 3 to5/minute that persists for �20 minutes.

Uterine Contractions

● Quantified as the number of contractions in a 10-minute window, averaged over 30 minutes.

Normal: �5 contractions in 10 minutesTachysystole: �5 contractions in 10 minutes

InterpretationA three-tier Fetal Heart Rate Interpretation system hasbeen recommended as follows:

● Category I FHR tracings: Normal, strongly predictiveof normal fetal acid-base status and require routinecare. These tracings include all of the following:

�Baseline rate: 110 to 160 beats/min�Baseline FHR variability: Moderate�Late or variable decelerations: Absent�Early decelerations: Present or absent�Accelerations: Present or absent

● Category II FHR tracings: Indeterminate, require evalu-ation and continued surveillance and reevaluation. Exam-ples of these tracings include any of the following:

�Bradycardia not accompanied by absent variability�Tachycardia�Minimal or marked baseline variability�Absent variability without recurrent decelerations�Absence of induced accelerations after fetal stimula-

tion�Recurrent variable decelerations with minimal or

Table 1. Arterial Umbilical Cord Gas ValuespH PCO2 (mm Hg) PO2 (mm Hg) Base Excess

Normal* >7.20 <60 >20 <�10(7.15 to 7.38) (35 to 70) (�2.0 to �9.0)

Respiratory Acidosis <7.20 >60 Variable <�10Metabolic Acidosis <7.20 <60 Variable >�10Mixed Acidosis <7.20 >60 Variable >�10

*Normal ranges from Obstet Gynecol Clin North Am. 1999;26:695

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moderate variability�Prolonged decelerations�Recurrent late decelerations with moderate variability�Variable decelerations with other characteristics,

such as slow return to baseline

● Category III FHR tracings: Abnormal, predictive ofabnormal fetal acid-base status and require promptintervention. These tracings include:

�Absent variability with any of the following:y Recurrent late decelerationsy Recurrent variable decelerationsy Bradycardia

�Sinusoidal pattern

Data from Macones GA, Hankins GDV, Spong CY,Hauth J, Moore T. The 2008 National Institute of ChildHealth and Human Development workshop report onelectronic fetal monitoring. Obstet Gynecocol. 2008;112:661–666 and American College of Obstetricians andGynecologists. Intrapartum fetal heart rate monitoring:nomenclature, interpretation, and general managementprinciples. ACOG Practice Bulletin No. 106. Washing-ton, DC: American College of Obstetricians and Gyne-cologists; 2009.

We encourage readers to examine each strip in thecase presentation and make a personal interpretation ofthe findings before advancing to the expert interpreta-tion provided.

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Case PresentationHistory

A 28-year-old G2P1 woman at 38–3/7 weeks’ gestationpresents to labor and delivery in early labor desiring a trialof labor after cesarean section (TOLAC). She is currentlycontracting every 6 minutes, with intact membranes, andis admitted for augmentation of labor. She reports posi-tive fetal movement and denies bleeding or leaking of

fluid. Her history includes gestational diabetes (con-trolled by diet), a previous cesarean section for arrest ofdilation at 3 cm, and a large-for-gestational age babyweighing 9 lb 8 oz. Her temperature is 36.8°C, heart rateis 78 beats/min, respiratory rate is 18 breaths/min, andblood pressure is 95/60 mm Hg. A cervical examinationis deferred at this time. An initial FHR tracing is obtainedshortly after admission (Fig. 1).

Figure 1. EFM Strip #1.

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Findings on EFM Strip #1 are:

● Variability: Moderate● Baseline Rate: 140 beats/min● Episodic Patterns: Accelerations● Periodic Patterns: None● Uterine Contractions: Irregular; mild-to-moderate in-

tensity per palpation● Interpretation: Category I tracing● Differential Diagnosis: Early labor with normal FHR tracing● Action: A Category I tracing may be following routinely

and does not require any interventions. Most investiga-tions that examined the probability of a successful vaginalbirth after cesarean (VBAC) in women attempting aTOLAC showed a 60% to 80% rate. (1) However,women whose first cesarean sections were indicated dueto arrest of labor and infant macrosomia (�4,000 to4,500 g), like this patient, were less likely to have success-ful VBAC than those whose first cesarean sections werefor nonrecurring causes such as a breech presentation. (1)This woman’s presentation at 38–3/7 weeks’ gestationwith an estimated fetal weight within the normal rangefor gestational age increases her chances of a successfulvaginal delivery. Regardless, evidence suggests thatwomen who have at least a 60% to 70% chance of VBAC

have similar or less maternal morbidity when they un-dergo TOLAC than women electing to have repeat ce-sarean sections (2) and should be counseled and offered aTOLAC, if appropriate. The patient must be given thechoice to have an elective cesarean section or a TOLACfollowing counseling. In addition to continuous fetalmonitoring, all staff must remain vigilant for potentialcomplications of TOLAC and watch for signs associatedwith uterine rupture, such as fetal bradycardia, increaseduterine contractions, vaginal bleeding, loss of fetal sta-tion, or new onset of intense uterine pain. (1) A fullobstetrical team capable of initiating an emergency cesar-ean delivery must be immediately available. Rapid deliv-ery of the fetus within 30 minutes or less will decrease therisk of fetal death and long-term neurologic disability inthe event of a uterine rupture.

Case ProgressionOver the next few hours, the patient receives early

epidural analgesia and oxytocin therapy, and her contrac-tions increase in intensity and frequency to every 2 min-utes. Vital signs remain within normal limits, and she isafebrile. A cervical examination reveals 1 cm dilation,70% effacement, and �2 station. Membranes are intact

Figure 2. EFM Strip #2.

Figure 1. EFM Strip #1.

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and oxytocin infusion is now at 10 MU/min. The FHRtracing remains a Category I, indicating a normal acid-base and a well-oxygenated fetus at this time. Four hourslater, cervical examination shows 5 cm dilation, 80%effacement, and a floating station. A fetal tracing isobtained (Fig. 2).

Findings on EFM Strip #2 are:

● Variability: Moderate● Baseline Rate: 140 beats/min● Episodic Patterns: Accelerations● Periodic Patterns: None● Uterine Contractions: Every 2 to 4 minutes; mild-to-

moderate intensity per palpation● Interpretation: Category I● Differential Diagnosis: Active labor with normal FHR

tracing. Consider uterine rupture (loss of station) ver-sus cephalopelvic disproportion (CPD).

● Action: A loss of fetal station is one of the signs of

uterine rupture, but the most common sign in up to70% of cases is an FHR abnormality. In this case, auterine rupture is highly unlikely due to the Category IFHR tracing that demonstrates a well-oxygenated fe-tus. The fetal loss of station most likely can be ex-plained by either a variation in cervical examiners or thefetal head floating due to CPD. Because the fetus isexhibiting a normal FHR with moderate variability,labor is allowed to progress, with continuous monitor-ing and close observation by staff.

Two hours later, results of a cervical examination docu-ment no changes, with 5 cm dilation and 80% efface-ment, but the station is now �2, allowing artificial rup-ture of the membranes. Clear fluid is noted. A fetal scalpelectrode (FSE) and intrauterine pressure catheter(IUPC) are inserted to assess FHR variability more accu-rately and quantify uterine activity and intrauterine pres-sure. The associated tracing is seen in Figure 3.

Figure 3. EFM Strip #3.

Figure 2. EFM Strip #2.

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Findings on EFM Strip #3 are:

● Variability: Moderate● Baseline Rate: 140 beats/min● Episodic Patterns: Accelerations● Periodic Patterns: Early decelerations● Uterine Contractions: Every 2 to 3 min, lasting 50 to

70 sec, 50 to 60 mm Hg● Interpretation: Category I● Differential Diagnosis: Active labor with normal FHR

tracing.● Action: The arrow on the fetal tracing indicates the

point at which the FSE was applied. Most often, anFSE is applied when it is difficult to obtain an adequatetracing due to fetal movement or maternal size or forconfirmation of a tracing that shows absent-to-minimalvariability. In this case, the tracing was already of goodquality and the application of an FSE made no differ-ence in the tracing appearance. The IUPC measuresintrauterine pressure in mm Hg on the tracing. Mon-tevideo units (MVUs) are used to evaluate uterineactivity using an IUPC. The measurement is calculated

by adding together the intensity in mm Hg (peak ofcontraction less baseline tone) of all contractions in a10-minute period. A contraction pattern totaling atleast 200 MVUs per 10-minute period is consideredadequate labor. When arrest of labor is considered,historically 2 hours with adequate MVUs was consid-ered sufficient time to allow before diagnosing an arrestof dilatation, but current evidence suggests that4 hours of uterine activity exceeding 200 MVU willresult in 92% vaginal delivery rate with no increased riskto the newborn. (3)

Over the next hour, the FHR tracing remains a CategoryI, with recurrent early decelerations. Contractions con-tinue every 2 minutes, with 180 MVUs. Maternal vitalsigns are within normal limits. The plan is to continue tomonitor FHR and uterine activity and recheck the cervixin 2 hours to rule out an arrest of dilatation. However,the findings on the FHR tracing obtained 1 hour later(Fig. 4) prompt a change in plans.

Figure 4. EFM Strip #4.

Figure 3. EFM Strip #3.

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Findings on EFM Strip #4 are:

● Variability: Moderate● Baseline Rate: Initially 140 beat/min, then indetermi-

nate due to prolonged deceleration● Episodic Patterns: Acceleration● Periodic Patterns: Variable deceleration followed by

prolonged deceleration● Uterine Contractions: Every 1 to 2 min, lasting 50 to

60 sec, 40 to 50 mm Hg● Interpretation: Category II● Action: This type of pattern occurs during an acute

hypoxic event, as indicated by the initial marked vari-ability followed by a prolonged deceleration to an FHRof 40 beats/min. The physician is called to the bedsidefor an immediate evaluation, oxytocin administration isdiscontinued, patient is re-examined to rule out a cordprolapse, and the cervix is found to be unchanged.Based on the sudden and severe fetal bradycardia andrisks associated with TOLAC, uterine rupture, andfetal risk of acidosis, the patient is taken to the operat-ing room for an urgent cesarean section.

OutcomeApproximately 9 minutes later, a viable female infantweighing 3,620 kg is delivered by cesarean section withApgar scores of 8 and 8 at 1 and 5 minutes, respectively.Cord gases indicate a mild respiratory acidosis (Table 2).Even though there was no evidence of a uterine rupture,the decision to deliver immediately was a good one andreflects a very efficient team that was well prepared toexpedite the delivery of the infant within minutes of theprolonged deceleration.

References1. American College of Obstetricians and Gynecologists (ACOG).Vaginal Birth After Previous Cesarean Delivery: Clinical Manage-ment Guidelines For Obstetrician-Gynecologists. ACOG Practice Bul-letin No. 115. Washington DC: American College of Obstetriciansand Gynecologists; 20102. Cahill AG, Stamilio DM, Odibo AO, et al. Is vaginal birth aftercesarean (VBAC) or elective repeat cesarean safer in women with aprior vaginal delivery? Am J Obstet Gynecol. 2006;195:1143–11473. Rouse D, Owen J, Savage K, Hauth J. Active phase labor arrest:revisiting the 2 hour minimum. Obstet Gynecol. 2001;98:550–554.

Figure 4. EFM Strip #4.

Table 2. Arterial Umbilical Cord Gas ValuespH PCO2 (mm Hg) PO2 (mm Hg) Base Excess

Normal* >7.20 <60 >20 <�10(7.15 to 7.38) (35 to 70) (�2.0 to �9.0)

Respiratory Acidosis <7.20 >60 Variable <�10Metabolic Acidosis <7.20 <60 Variable >�10Mixed Acidosis <7.20 >60 Variable >�10Patient 7.092 72 14 �8

*Normal ranges from Obstet Gynecol Clin North Am. 1999;26:695

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DOI: 10.1542/neo.12-10-e5982011;12;e598NeoReviews 

Maurice L. Druzin and Nancy PetersonStrip of the Month: October 2011

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