Frequency of Fetal Heart Rate Categories and.6

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Frequency of Fetal Heart Rate Categoriesand Short-Term Neonatal Outcome

Marc Jackson, MD, Calla M. Holmgren, MD, M. Sean Esplin, MD, Erick Henry, MPH,and Michael W. Varner, MD

OBJECTIVE: To estimate the time spent in each fetalheart rate category during labor and during the last 2

hours before delivery in term singleton pregnancy and to

estimate the relationship between the time spent in each

category and short-term neonatal outcomes.

METHODS: This study reviewed fetal heart rate data and

newborn outcomes of women in term labor in 10 hospi-tals over 28 months. Fetal heart rate characteristics were

assessed by labor and delivery nurses, and categories

were assigned by computer using definitions from theEunice Kennedy ShriverNational Institute of Child Health

and Human Development. The duration of time in each

category was calculated and correlated with newborn

outcome.

RESULTS: Forty-eight thousand four hundred forty-fourpatients were identified. Considering all of labor, cate-

gory I was present 77.9% of the time, category II waspresent 22.1% of the time, and category III was present

0.004% of the time. In the last 2 hours before delivery,category I decreased to 60.9% of the duration, category IIincreased to 39.1%, and category III increased to 0.006%.Newborns of women whose last 2 hours were exclusivelycategory I did well; only 0.6% had 5-minute Apgar scoresless than 7, and 0.2% had low Apgar scores with neonatalintensive care unit (NICU) admission. When more than75% of the last 2 hours was category II, low 5-minute

Apgar score increased to 1.3% of patients, and low

5-minute Apgar score with NICU admission increased to

0.7% (both P


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and validation of the assumptions regarding fetalstatus with the new fetal heart rate categories. To date,few descriptive data are available to address thesequestions.

The objectives of this study were to estimate theamount of time spent in each of the NICHD fetalheart rate categories during labor and during thelast 2 hours of labor in term singleton pregnancyand to estimate the relationship between the dura-tion of time spent in each category and short-term

neonatal outcomes.

MATERIALS AND METHODSWe performed a review of the intrapartum fetal heartrate characteristics of all patients with a singleton,nonanomalous fetus in term labor at 10 Intermoun-tain Healthcare hospitals between March 1, 2007, andJune 30, 2009. Patient inclusion criteria included:singleton pregnancy; gestational age 37.0 weeks orgreater; in labor (either spontaneous or induced) withfetal heart rate monitoring for at least 120 minutes;

and delivery during the monitoring period. Patientswhose fetus or newborn had a structural or geneticabnormality were excluded. Patients admitted for sched-uled cesarean delivery were excluded, even if they weremonitored for more than 2 hours before surgery.

All study hospitals used electronic fetal monitor-ing in labor, and all labor and delivery nurses were

specifically trained using standardized protocols inthe reading of fetal heart rate monitor tracings. Beforebeginning work on an Intermountain Hospital laborand delivery suite, nurses complete a 4-hour class-room session in basic fetal heart rate monitoring.Within the first year, they must then successfullycomplete a 2-day course in fetal heart rate monitoringthat was developed and is sponsored by the Associa-tion of Womens Health, Obstetric and NeonatalNurses; this course includes a day of lecture materialsand a day of skills demonstration and testing. There-after, each nurse must document continuing educa-

tion in fetal heart rate interpretation. This ongoingtraining consists of attending at least two fetal heartrate Strip Review classroom presentations and com-pleting at least 10 online self-study sessions usingIntermountains Strip of the Month each year.

All intrapartum fetal heart rate monitor tracingswere read by a labor and delivery nurse at least every20 minutes and the fetal heart rate characteristics(Box 2) entered into a bedside computer workstation.Whenever a change in fetal heart rate patterns devel-oped (eg, onset of variable decelerations or change infetal heart rate baseline), the nurse entered the newcharacteristics into the workstation, even if fewer than20 minutes had passed since the last entry. If therewere no further changes, the next assessment and dataentry was 20 minutes later. If there were additionalfetal heart rate changes observed sooner, the newcharacteristics were entered at the time of change.Thus, the duration of time of each characteristic and,therefore, each fetal heart rate category was tracked inreal time rather than in blocks of time. The fetal heart

Box 1. Three-Tier Fetal Heart Rate ClassificationSystem

Category I

Category I fetal heart rate patterns include all of thefollowing:

Baseline rate of 110160 beats per minute

Moderate baseline fetal heart rate variability

Late or variable decelerations are absent

Early decelerations may be present or absent

Accelerations may be present or absent

Category II

Category II fetal heart rate tracings include all patternsnot categorized as category I or category III

Category III

Category III fetal heart rate patterns include:

Absent baseline fetal heart rate variability with any of thefollowing:

Recurrent late decelerations

Recurrent variable decelerations

Bradycardia

Sinusoidal pattern

Modified from Macones GA, Hankins GDV, Spong CY, HauthJ, Moore T. The 2008 National Institute of Child Health andHuman Development workshop report on electronic fetalmonitoring: update on definitions, interpretation, andresearch guidelines. Obstet Gynecol 2008;112:6616.

Box 2. Fetal Heart Rate Characteristics Assessed

Baseline fetal heart rateFetal heart rate variabilityPresence of accelerationsPresence of variable decelerations

IsolatedRecurrent

Presence of late decelerationsPresence of bradycardiaPresence of tachycardia

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rate tracing and the entered data were then stored ina systemwide enterprise data warehouse and linked tomaternal and short-term neonatal data.

Fetal heart rate characteristics on all patients wereretrieved from the data warehouse, and software wasdeveloped to convert the data on fetal heart ratecharacteristics into the appropriate NICHD fetal

heart rate category at each reading. Because nursingentries were timed, the duration of time in fetal heartrate category could then be calculated.

Descriptive statistics were performed on fetalheart rate category data for all patients from the entiremonitoring period and from the last 2 hours ofmonitoring before delivery. Proportions were com-pared using chi-square testing with Yates correction.P.01 was considered statistically significant. Theinvestigation was approved by the IntermountainHealthcare institutional review board.

RESULTSA total of 48,444 women met criteria for inclusion.The number of study patients from the 10 hospitalsranged from 1,982 to 7,239 during the 28-monthsampling period. The majority of the patients werewhite, married, and parous. The mean maternal agewas 27.0 years, the mean time monitored was 513.1minutes, the median time monitored was 432.4 min-utes, and the range of monitoring time was 120.05,578.3 minutes. The demographics of the entiregroup are detailed in Table 1.

Labor was spontaneous in 25,590 (52.8%) pa-tients, induced for a medical or obstetric indication in10,704 (22.1%), and electively induced in 12,150(25.1%). Oxytocin was used, either for induction oraugmentation of labor, in 24,825 (51.2%) patients.

Overall, category I fetal heart rate patterns wereobserved at some point in 48,191 (99.5%) of tracings,

category II patterns were found in 40,758 (84.1%) oftracings, and category III patterns were seen in 54(0.1%) of tracings. A large majority, 83.6%, of patientshad a mix of categories during their labor. Only 7,686(15.9%) patients had monitor strips with category Ifetal heart rate patterns exclusively, 253 (0.5%) hadonly category II patterns, and no patients (0.0%) hadonly category III fetal heart rate.

Examining the entire duration of monitoring inall patients, the fetal heart rate pattern was classifiedas category I 77.9% of the time, as category II 22.1%of the time, and as category III 0.004% of the time.

Segmenting the study population by parity, nulliparasspent a slightly smaller proportion of time in categoryI and slightly greater time in category II during theirlabors compared with multiparas (Table 2).

In the 2 hours before delivery, category I tracingsbecame less common, and category II and categoryIII tracings became more common. Among all pa-tients in the last 2 hours of monitoring, category Itracings were present 60.9% of the time, category IItracings were present 39.1% of the time, and categoryIII tracings were seen 0.006% of the time (Table 2).

The group whose entire labor was spent in fetalheart rate category I had good outcomes. Only 290(3.8%) had 1-minute Apgar scores less than 7, and 46(0.6%) had 5-minute Apgar scores less than 7. Therewere 249 (3.2%) neonatal intensive care unit (NICU)admissions in this group. Only 14 (0.2%) neonates hadlow 5-minute Apgar scores and NICU admission. Out-comes were similar in the group whose last 2 hours oflabor was solely in fetal heart rate category I with anincreased incidence of low 1-minute Apgar score but nodifference in the other neonatal outcomes (Table 3).

To assess whether the amount of time spent in

category II was related to short-term neonatal out-come, patients were divided into subgroups based onthe amount of time that was spent in category IIduring the last 2 hours before delivery. Patients whospent the entire last 2 hours of labor in category I werecompared with those who spent increasing time incategory II, divided into quartiles of 125%, 2650%,5175%, and 76100% of the last 2 hours in fetalheart rate category II.

There was no difference between these subgroupswith respect to maternal age, race, marital status, or

Table 1. Demographics of the Study Population

Mean age (y) 27.0Ethnicity

White 81.4Hispanic 12.1Pacific Islander 0.9Asian 1.1African American 0.6Other or unknown 3.9

ParityNulliparous 39.7

Multiparous 60.3Married 82.6Medical or obstetric complication* 10.2Tobacco use 3.2Mean time monitored (min)

All patients 513.1Nulliparas 675.0Multiparas 406.6

Data are % unless otherwise specified.* Includes chronic hypertension, gestational hypertension,

pregestational diabetes, gestational diabetes, preeclampsia,suspected intrauterine growth restriction, oligohydramnios,placental abruption, or all.

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tobacco use. However, with increasing time in cate-gory II above 25% of the last 2 hours of labor,nulliparity and medicalobstetric complications weremore common (both P.01; Table 4).

Increasing time in category II in the last 2 hoursof labor also was associated with increased likelihoodof NICU admission or Apgar score less than 7 but notuntil more than 50% of the time was spent in fetalheart rate category II. In the 5175% category IIquartile, only the likelihood of a low 1-minute Apgarscore and the likelihood of NICU admission were

increased (both P.01). However, in the 76100%category II quartile, there was an increased likelihoodof 1-minute Apgar score less than 7, 5-minute Apgarscore less than 7, NICU admission, and the combina-tion of NICU admission and 5-minute Apgar scoreless than 7 (all P.001; Table 4).

DISCUSSIONThere is a broad consensus as to the definition of anormal intrapartum fetal heart rate pattern: normalbaseline, moderate variability, and absence of vari-able or late decelerations.3,4 Category I fetal heart ratepatterns are assumed to be reflective of normal fetaloxygenation status, and bad outcomes are uncom-mon. Our data confirm this notion. Among patientswhose fetal heart rate patterns in the last 2 hoursbefore delivery were exclusively category I, only 0.2%(one in every 531) had low 5-minute Apgar scores and

admission to the NICU.Similarly, there is accord on abnormal fetal heart

rate characteristics: absent variability, recurrent lateor variable decelerations, prolonged bradycardia, andsinusoidal patterns.3,4 Fortunately, category III fetalheart rate patterns are a very rare event. In ourpopulation of patients in term labor, category III wasidentified in only 0.1% of patients (one in every 897).

Between the extremes, category II fetal heart ratepatterns are very common, occurring in 84% oflabors. The proportion of time spent in category II

increases in the 2 hours before delivery. There is anincreased likelihood of adverse short-term outcomeswith increasing time in category II fetal heart ratepatterns.

Despite the association between increasing timein category II and low Apgar scores and NICUadmission, the huge majority of newborns who hadpredominantly category II tracings experienced noshort-term morbidity. Thus, describing category II asindeterminate is appropriate. However, its high fre-quency and broad range of outcomes diminish the

Table 3. Newborn Outcomes in Patients WithCategory I Tracings

All FHR Category I

EntireLabor

Last 2 hof Labor

No. of patients 7,686 11,6771-min Apgar score less than 7 290 (3.8) 566 (4.8)*5-min Apgar score less than 7 46 (0.6) 71 (0.6)NICU admission 249 (3.2) 459 (3.9)5-min Apgar score less than 7

and NICU admittance14 (0.2) 22 (0.2)

FHR, fetal heart rate; NICU, neonatal intensive care unit.Data are n (%) unless otherwise specified.* P.001 compared with entire labor FHR category I.

Table 2. Distribution of Fetal Heart Rate Category Time in Labor

Overall Labor Monitoring Last 2 h of Labor

Category I Category II Category III Category I Category II Category III

All patientsMean minutes 399.6 113.5 0.02 73.1 46.9 0.01Percentage of total 77.9 22.1 0.004 60.9 39.1 0.006Median minutes 339.4 74.8 0.0 80.0 40.0 0.0

Range 04,924.3 01,740.9 069.0 0120.0 0120.0 037.0Nulliparous

Mean minutes 514.5 160.4 0.03 66.1 53.9 0.01Percentage of total 76.2 23.8 0.004 55.1 44.9 0.009Median minutes 441.2 121.0 0 69.3 50.7 0.0Range 03,962.5 01,691.6 066.2 0120.0 0120.0 037.0

MultiparousMean minutes 324.0 82.7 0.01 77.7 42.2 0.01Percentage of total 79.7 20.3 0.003 64.8 35.2 0.005Median minutes 287.9 54.0 0.0 86.5 33.5 0.0Range 04,924.3 01,740.9 069.0 0120.0 0120.0 028.0

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usefulness of category II fetal heart rate patterns as an

indicator of fetal condition. This is reflected in therecommendations for management of category IItracings, which stress evaluation, continued surveil-lance, initiation of appropriate corrective measureswhen indicated, and reevaluation.5

Others have addressed the diversity found in theindeterminate category of fetal heart rate tracings.Larma and colleagues examined fetal heart rate char-acteristics in the last hour before delivery of 107neonates with documented umbilical cord acidosisand compared them with those of a control groupwith normal blood gas results. They found differencesin baseline rate, bradycardia, variability, and reactiv-ity between acidotic newborns with and withouthypoxicischemic encephalopathy. However, the fe-tal heart rate characteristics discriminated poorly be-tween acidotic and nonacidotic newborns, becausethe frequency of accelerations, decelerations, variabledecelerations, and severe variable decelerations werenot different between the two groups.6

Parer and Ikeda have recognized that broad fetalheart rate categories will necessarily include a widerrange of outcome severities. Basing their classification

system on published outcome risks related to specificfetal heart rate characteristics, they proposed a color-coded, five-category scheme, essentially dividing theindeterminate category into three additional risk lev-els.7 Although their system is rather complex, a studyof tracing reviews found good agreement betweenblinded, expert readers.8 Also noting that such asystem lends itself well to computer-based interpreta-tion, they showed that a software-based fetal heartrate assessment system correlated well with the hu-man experts.8

The large number of patients, managed in both

tertiary and community hospitals, is a strength of ourstudy. The ongoing training in fetal heart rate moni-toring provided to all labor and delivery clinical staffis an additional strength. Also, our data set links tospecific patient outcomes rather than to literature-based risks. Our study has several disadvantages. Oneis the retrospective nature of the data. There is apossibility of distortion of our results through censor-ing by intervention, because there may have beenexpedited delivery in some cases with more pro-longed nonreassuring category II patterns. Thiswould likely decrease morbidity in the category IIgroup but reflects a real-world assessment of theassociations between fetal heart rate and outcome.More significantly, there is a lack of umbilical cordblood gas data; cord gas sampling is not required inroutine deliveries in the Intermountain Healthcaresystem, and Apgar scores and NICU admission areused as functional markers for neonatal hypoxia.

The use of intrapartum fetal heart rate monitoringas a screening test has been rightly questioned.9 In ourdata set, there are more than 40 combinations of fetalheart rate characteristics that qualify a fetal heart rate

pattern as category II. Combining so many differentfetal heart rate patterns into a single indeterminatecategory surely detracts from the use of fetal heart ratemonitoring as an indicator of fetal condition. Futureresearch should focus on the subcharacterization ofcategory II fetal heart rate tracings, the cumulativeeffect of the duration of unfavorable fetal heart ratecharacteristics, and the effects of other risk factors todifferentiate those at highest risk from those at lowrisk for neonatal compromise and so to improve thepredictive value of fetal heart rate monitoring.

Table 4. Maternal Variables and Short-Term Neonatal Outcomes With Increasing Time in Fetal HeartRate Category II

Time in Category, Last 2 h of Labor

All FHRCategory I

125%Category II

2650%Category II

5175%Category II

76100%Category II

No. of patients 11,676 9,313 9,846 8,115 9,494Percentage of total 24.1 19.2 20.3 16.8 19.6

Nulliparity (%) 34.8 33.8 36.5* 42.9* 52.6*Medical or obstetric complication (%) 8.1 8.7 9.2* 10.4* 11.7*1-min Apgar score less than 7 566 (4.8) 451 (4.8) 536 (5.4) 545 (6.7)* 922 (9.7)*5-min Apgar score less than 7 71 (0.6) 56 (0.6) 61 (0.6) 69 (0.9) 119 (1.3)*NICU admission 459 (3.9) 363 (3.9) 424 (4.3) 395 (4.9)* 691 (7.3)*5-min Apgar score less than 7 and

NICU admittance22 (0.2) 22 (0.2) 27 (0.3) 24 (0.3) 67 (0.7)*

FHR, fetal heart rate; NICU, neonatal intensive care unit.Data are n (%) unless otherwise specified.* P.001 compared with all FHR category I.

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Frequency of Fetal Heart Rate Categories and.6