Intrapartum Electronic Fetal Monitoring
Lisa A. Miller
Donna J. Ruth
Part 1 Introduction and Overview
This module will provide clinicians with practical information on intrapartum fetal monitoring, with a primary focus on electronic fetal monitoring (EFM). The module is divided into six sections. Part 1 provides an overview of intrapartum fetal monitoring and includes information on the history of fetal monitoring, differences between intermittent auscultation (IA) and EFM, and the equipment and methods for both modalities. Parts 2 and 3 cover definitions, basic physiology, and offer a standardized approach to interpretation and management of EFM, while Part 4 provides information on umbilical cord gas analysis. Documentation is reviewed in Part 5, and Part 6 concludes this module with a self-assessment. The module has been written as a concise and practical guide to daily clinical practice, and is not meant to be an authoritative treatise on either EFM or IA. Clinicians are encouraged to obtain ongoing continuing education in fetal monitoring, and to regularly review the literature as part of the maintenance of professional practice.
Intrapartum Fetal Monitoring
Intrapartum fetal monitoring consists of the assessment and evaluation of fetal status during labor. During the intrapartum period, information related to both fetal heart rate (FHR) and uterine activity (UA) is obtained and interpreted to assist clinicians in three primary areas: (1) the evaluation of fetal oxygenation; (2) the application of conservative corrective measures; and (3) the ongoing management of labor and provision of appropriate labor support. Fetal monitoring may be done by IA, EFM, or a combination of both, but all laboring patients should have some type of ongoing evaluation over the course of labor.
Historically, monitoring of the FHR by auscultation has been in existence for over 200 years. The use of the electronic fetal monitor began in the late 1960s. Over the last several decades, the use of EFM has become ubiquitous in hospital labor and delivery settings.1,2,3 But the routine use of EFM (especially continuous EFM throughout labor) is being questioned today, especially for low-risk patients. A systematic review of 13 randomized trials that included >37,000 women of varying risk status and compared continuous EFM to IA found no significant difference in the majority of outcomes including perinatal mortality, cerebral palsy, hypoxic ischemic encephalopathy (HIE), and neonatal intensive care unit (NICU) admission. While the review did demonstrate decreased incidence of neonatal seizures in the continuous EFM group, there were no differences in neurodevelopmental impairment at ≥12 months of age, and 661 women would need to be monitored in labor to prevent one neonatal seizure. The review also noted that continuous EFM is associated with significantly higher rates of cesarean and operative vaginal deliveries.4
Although it may seem that the results of systematic analysis would point to the complete abandonment of EFM for all patients, clinicians must understand some of the limitations of the current state of the science regarding EFM. These include the following:
Only 2 of the 13 randomized trials in the systematic review were of high quality.
None of the randomized trials utilized standardized nomenclature, interpretation, or management.
Most of the trials did not include high-risk patients, so the safety of IA is not clear in the high-risk population, where continuous EFM continues to be recommended.1
The vast majority of cases of cerebral palsy are related in whole or in part to antepartum events, not intrapartum events, and therefore the lack of a reduction in cerebral palsy related to EFM use is not an unexpected finding.5
When used as a diagnostic tool for the development of cerebral palsy, the false-positive rate of EFM may be as high as 99.8%5; but no trials to date have compared IA to application of EFM as a screening tool.
While EFM has failed as a diagnostic tool, the value of EFM as a screening tool during the intrapartum period should not be lightly dismissed. There is wide consensus regarding the negative predictive value of two EFM components. The presence of either moderate FHR variability or an FHR acceleration provides reliable evidence to exclude the possibility of hypoxia-related central nervous system depression.6,7 Combined with an understanding of basic fetal oxygenation, normal versus abnormal uterine activity, and the importance of clinical context, EFM used as a screening tool can assist clinicians in safe and effective labor support and assessment of fetal response to labor; intervening appropriately to correct interruption of oxygenation and, when necessary, proceeding with expedited delivery prior to the deterioration of fetal acid–base status. As Clark et al. correctly point out, “one important goal of intrapartum care is delivery of the fetus, when possible, prior to the development of damaging degrees of hypoxia/acidemia.”6
Regardless of the ongoing debate regarding EFM versus IA, the use of EFM remains very common in many labor and delivery units. Clinicians need to be skilled in both EFM and IA to safely care for the variety of patients cared for in contemporary birth settings. Ultimately, the decision as to which monitoring method is used should be a joint decision between patients and healthcare providers. Factors that influence this decision may include clinical situation and risk status, availability of equipment, unit staffing patterns, and knowledge and skill level of staff (in the selected monitoring method). It has been suggested that informed consent be obtained before the initiation of any type of fetal monitoring8,9; however, clinicians should understand that when discussing options with patients, there are only two choices, IA and EFM, as no studies have been performed (nor are any likely) to compare monitoring versus no monitoring during labor. Regardless of which method of monitoring is chosen, each unit should have written policies and guidelines for both IA and EFM that are in accordance with guidelines endorsed by professional organizations such as the American Congress of Obstetrics and Gynecology (ACOG), the Association of Women’s Health, Obstetric, and Neonatal Nurses (AWHONN), and the American College of Nurse-Midwives (ACNM). Unit guidelines should clearly list the procedures to be followed when using the chosen monitoring technique, define the standard terminology to be used for each method, and include the required frequency of assessments.10 See Table 7.1 for the recommended frequency of assessment based on the phase and stage of labor. It is important to note that the recommended frequencies of assessments in latent phase of labor have not been established, and until further research is available, clinicians may be wise to comply with the standards set for active phase rather than choose an arbitrary standard.
TABLE 7.1 GUIDELINES FOR ASSESSMENT OF FETAL HEART RATE | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| |||||||||||||||||||||
Guidelines for Assessment of Fetal Heart Rate10
Intermittent Auscultation (IA)
While IA is not the primary focus of this module, it will be briefly reviewed here for two important reasons: (1) it may be the primary method of fetal assessment in labor for low-risk women following proper informed consent; and (2) it is the only alternative to EFM, making it an appropriate and necessary adjunct for situations where obtaining an interpretable EFM tracing is difficult. IA involves monitoring the FHR, through the use of either a fetoscope or Doppler, at specified intervals. IA allows for assessment of the FHR without belts, patches, or cables, and this means greater maternal mobility. Therefore, IA may be much more comfortable for the laboring woman, as well as promote a more natural, less technological environment for birth.
IA has been found to be a safe and reasonable option for monitoring low-risk women during uncomplicated labor when performed by a practitioner who:
IA has been found to be a safe and reasonable option for monitoring low-risk women during uncomplicated labor when performed by a practitioner who:
is experienced in the labor and delivery setting and competent in the use of IA;
can discern, by auditory means, significant changes in the FHR;
is practiced in palpating uterine contraction and relaxation;
is capable of initiating appropriate interventions when indicated.11
Components Assessed with Intermittent Auscultation
In general, baseline rate and baseline rhythm can both be evaluated using IA. Baseline rate is assessed between contractions and during periods when the fetus is not active. In addition, baseline variations such as tachycardia (rate greater than 160 beats per minute [bpm]) and bradycardia (rate less than 110 bpm) can be readily identified. If tachycardia or bradycardia is suspected, then more frequent assessments may be warranted to determine if a baseline change has occurred or if the increase or decrease in rate was temporary. Auscultation can also be used to detect transient increases and decreases in the FHR, but adequacy of accelerations and types of decelerations based on current nomenclature cannot be confirmed without the visual assessment of an EFM tracing, as IA is a solely auditory assessment.
Baseline rhythm (regular or irregular) can also be evaluated with auscultation. Actual heart sounds can be heard using a stethoscope, fetoscope, or Pinard stethoscope. Doppler can be used to identify baseline rhythm, but the sound produced by the Doppler device is a representation of, not the actual, heart sounds. Auscultation may be used to verify the presence of a dysrhythmia.11 If an irregular rhythm is heard, alternative methods of assessment, such as ultrasound or fetal echocardiogram, may be indicated to determine the type of dysrhythmia present. The majority of dysrhythmias discovered in the intrapartum period are benign and do not require intervention other than notification of the pediatric service for appropriate follow-up of the newborn.
Performance of Intermittent Auscultation
Follow these steps when performing IA:
Explain the procedure to the laboring woman.
Determine fetal position using Leopold’s maneuvers.
Palpate the uterus to assess for contractions and resting tone. This helps the practitioner to assess the FHR response to uterine activity.
Apply the fetoscope or Doppler device on the maternal abdomen over where the fetal back is located (this is typically where fetal heart sounds will most audible).
Auscultate the FHR between contractions, beginning immediately after the end of the contraction and listening for at least 30- to 60-second intervals to determine the FHR and rhythm and response to uterine activity.
Count the maternal pulse to differentiate between fetal and maternal heart rates.
Document your assessments.
Share your findings with the laboring woman.
Assessment of fetal heart tones should be performed before:
induction or augmentation of labor with oxytocin;
initiation of anesthesia;
administration of medications;
ambulation;
artificial rupture of membranes (amniotomy);
transfer or discharge.
Assessment of the fetal heart tones should be performed after:
rupture of membranes (either spontaneous or artificial);
ambulation;
vaginal examination;
excessive uterine activity;
change in oxytocin dosage;
change in analgesia and anesthesia dosing;
admission to the labor and delivery unit.
Advantages/Benefits of Intermittent Auscultation
Patient comfort—the woman may be up and about and may move easily in bed. Sometimes the abdominal area and the lower back of a laboring woman are extremely sensitive. Belts
and other equipment can cause irritation and discomfort and interfere with her ability to concentrate and relax.
Facilitation of ambulation—ambulation often contributes to greater patient comfort and perhaps more rapid progress in labor. Freedom of movement (i.e., the ability to walk and stand) is supported by IA.
Requirement of caregiver to be at the bedside—this provides many benefits, such as comfort, support, and encouragement. The so-called doula effect, the presence of continuous labor support, has been shown to be of clear benefit to laboring women,12 and is a critical component of intrapartum care for all patients, regardless of risk status. With IA, close, frequent contact between the patient and caregiver occurs routinely.
Less technology—women who desire an atmosphere in which birth is viewed as a normal, natural event might prefer this method of monitoring. The ACNM supports a judicious use of technology in labor, including avoidance of unnecessary use of technology, and specifically states that “use of technology may be influenced by a woman’s preferences, and in the absence of clear evidence for use or avoidance of a certain intervention, a woman’s choice should prevail.”9
Neonatal outcomes—outcomes are comparable to those with EFM, at least in the low-risk population.
Lower cesarean birth rates—cesarean birth rates are lower in comparison with EFM as studied to date.
Equipment—equipment required for IA is less costly than that necessary for EFM.
Disadvantages/Limitations of Intermittent Auscultation
Practitioner skilled in auscultation—auscultation skills are required to perform assessments. Competency in the performance of auscultation should be demonstrated before the provision of care.
Nurse-to-patient ratio of 1:1—the nurse-to-patient ratio must be 1:1 and auscultation must occur on a regular basis for IA to be comparable to EFM. Nursing shortages and unit staffing patterns may sometimes preclude this capability.
Invasion of personal space—because very frequent, close personal contact is required to provide adequate assessment through IA, there may be some women who feel as if their personal space is being invaded.
Rapid heart rates (greater than 160 bpm)—heart rates greater than 160 bpm may be difficult to accurately count.
Inability to evaluate certain aspects of the FHR—examples include variability and the ability to discern the type of deceleration heard.
Physical limitations of equipment—maternal obesity, fetal position, and hydramnios may interfere with the practitioner’s ability to adequately assess the FHR by IA.
Documentation of FHR Obtained by Intermittent Auscultation
Documentation of auscultation findings must be done with each assessment. Each entry should include baseline rate and rhythm, the presence or absence of changes (increases or decreases) in the baseline rate. Other information that should be documented includes any change in patient status, all nursing interventions and patient responses, and any communication that occurs with healthcare providers.
Electronic Fetal Monitoring
EFM is the primary focus of this module, specifically its use during the intrapartum period. EFM is an electronic method of providing a continuous visual record of the FHR and obtaining information about the laboring woman’s uterine activity (Fig. 7.1). This information, which is recorded on graph paper, allows an ongoing minute-to-minute assessment of the FHR during labor. It also provides a permanent medical record, whether on paper or via electronic archiving.
NOTE: At the onset of EFM, validation of the equipment should be performed by auscultation of the FHR with a non mechanical means such as the fetoscope, and testing of the internal circuitry of the fetal monitor is accomplished by pushing the “test” button on the monitor and examining the test lines on the graph paper.
 FIGURE 7.1 The electronic fetal monitor. |
Indications for Electronic Fetal Monitoring
IA may not be appropriate for all labors.1,9,10 Many factors can influence the decision to use EFM during labor, and whether EFM should be continuous or intermittent (alternated with IA). Antepartum risk factors are those that the woman either enters her pregnancy with (such as chronic hypertension) or develops during the antepartum period (such as gestational diabetes). Other indications for monitoring may not appear until the woman is already in labor; these factors are considered intrapartum risk factors.
Antepartum risk factors include the following:
|
Intrapartum risk factors include the following:
|
EFM Equipment: External versus Internal
The electronic fetal monitor may be used in three different ways:
External fetal monitoring, also called indirect fetal monitoring, or noninvasive fetal monitoring. This method involves the use of an ultrasonic transducer to monitor the fetal heart while the contraction pattern is monitored with a tocodynamometer. Both are placed on the woman’s abdomen and are secured in place by elastic belts (Fig. 7.2).
The ultrasonic transducer, more commonly known as an ultrasound or Doppler, transmits high-frequency sound waves that detect movement within the fetal heart. The signal, which is similar to sonar used in submarines, is reflected back from moving structures and
is recognized by the machine as a cardiac event. The movement detected is both ventricular contraction and the actual opening and closing of valves within the heart.
is recognized by the machine as a cardiac event. The movement detected is both ventricular contraction and the actual opening and closing of valves within the heart.
 FIGURE 7.2 The external fetal monitor. |
The tocodynamometer, more commonly known as a toco, provides information about the laboring woman’s contraction pattern by detecting changes in the shape of the abdominal wall. It is usually placed directly over the uterine fundus. These changes in shape are the direct result of the effects of the uterine contraction on the contour of the maternal abdomen.
As a result of the manner in which the data are obtained, these methods are referred to as indirect or external monitoring because the techniques are performed external to the fetus and uterus. Because the vagina, cervix, and uterus are not invaded when applying an external monitor, the technique is also termed noninvasive.
External fetal monitoring may also be performed noninvasively by abdominal fetal electrocardiogram (fECG) (to capture FHR) and electromyogram (to capture uterine activity). This technology is not yet widely used, but may be superior to traditional external monitoring in patients with an elevated body mass index (BMI) where Doppler and tocotransducer use can be challenging.
Internal fetal monitoring is also called direct fetal monitoring or invasive fetal monitoring. With this method, the FHR is monitored by the use of a fetal spiral electrode (FSE), which is applied directly to the presenting part of the fetus, while the contraction pattern is monitored by the use of an intrauterine pressure catheter (IUPC) inserted vaginally into the intrauterine cavity through the cervix (Fig. 7.3). Note that a combination of internal and external monitoring may be used in some cases (Figs. 7.4 and 7.5).
 FIGURE 7.3 The internal fetal monitor. |
 FIGURE 7.4 Combination of external and internal monitoring. The tocodynamometer and helix/fetal scalp electrode are used together. |
 FIGURE 7.5 Combination of external and internal monitoring. The ultrasonic transducer and intrauterine pressure catheter are used together. |
 FIGURE 7.6 Determination of fetal heart rate with the use of a fetal scalp electrode. |
The FSE tracks the FHR by picking up R waves on the fECG. The interval between each R wave is measured and processed by internal circuitry and calculated to a rate in bpm; the result is printed on graph paper (Fig. 7.6). During a vaginal examination, the examiner attaches the spiral electrode or FSE, directly to the presenting part of the fetus (Figs. 7.7 and 7.8). The FSE is then secured to a leg plate/pad that has been attached to the woman’s thigh and connected to the monitor. FSE may be used when continuous information is required and a satisfactory tracing cannot be accomplished with external monitoring. Use of the FSE should be avoided in women who are HIV positive, have chronic or active hepatitis, have herpes simplex virus, or have a known and untreated sexually transmitted disease.13
 FIGURE 7.7 Components of the fetal scalp electrode. |
 FIGURE 7.8 Application of a fetal scalp electrode to the presenting part of the fetus. |
 FIGURE 7.9 Insertion of intrauterine pressure catheter. |
To monitor contractions internally, the IUPC is inserted through the cervix into the uterus beside the presenting part of the fetus (Fig. 7.9). The IUPC is used to determine the actual pressure inside the uterus during contractions, as well as the intrauterine pressure during relaxation time, which is called resting tone or tonus (Fig. 7.10). Changes in pressure at the tip of the
catheter (inside the uterus) are transmitted along the catheter. These pressure changes are caused by the force or intensity of the contractions and are translated into an electrical signal that is converted to a pressure reading expressed in mm Hg. This measurement is then displayed on the monitor. When clinical situations arise that require more precise measurements of uterine activity, an internal pressure catheter may be the preferred method of uterine monitoring.
catheter (inside the uterus) are transmitted along the catheter. These pressure changes are caused by the force or intensity of the contractions and are translated into an electrical signal that is converted to a pressure reading expressed in mm Hg. This measurement is then displayed on the monitor. When clinical situations arise that require more precise measurements of uterine activity, an internal pressure catheter may be the preferred method of uterine monitoring.
 FIGURE 7.10 Intrauterine pressure catheter. |
Points to remember when using the IUPC include the following:
When the IUPC is inserted, if resistance is met, the catheter must be slightly withdrawn and repositioned before insertion is attempted again.
IUPCs must be “zeroed” to calibrate the instrumentation. (Zeroing means that the instrument is calibrated to air pressure so that pressure changes in the uterus can be compared against a baseline measurement.)
The Fetal Monitor Tracing
Figure 7.11 illustrates monitor paper. This graph is marked in specific time intervals of 3 minutes to allow easy readability (paper speed should be set at 3 cm/min, which is standard in the
United States). Each small box represents 10 seconds. The numbers at the top of the strip in Figure 7.12 are reference numbers. They are sequential and appear at set intervals. On newer machines, these numbers may be located just above the uterine graph. These numbers assist in charting specific events by identifying their location on the strip. They also assist in chronologically reassembling a strip that has been separated for closer inspection.
United States). Each small box represents 10 seconds. The numbers at the top of the strip in Figure 7.12 are reference numbers. They are sequential and appear at set intervals. On newer machines, these numbers may be located just above the uterine graph. These numbers assist in charting specific events by identifying their location on the strip. They also assist in chronologically reassembling a strip that has been separated for closer inspection.
 FIGURE 7.11 Graph monitor paper. |
 FIGURE 7.12 Sequential numbering of strip graph paper. |
The strip is divided into two sections: an upper section and a lower section (Fig. 7.13). The upper section is the portion of the graph on which the FHR appears. The lower section is the portion of the graph on which the contractions, or uterine activity, are recorded. The FHR (upper) section of the graph is divided vertically by dark lines, with five light, vertical lines between every two dark lines (Fig. 7.14). The time interval between any two dark lines is 1 minute; therefore, the time interval between any two light lines is 10 seconds. This section of the graph is also divided horizontally by dark lines, with two light, horizontal lines between
every two darker lines (Fig. 7.15). There is a horizontal column of numbers ranging from 30 to 240. These are reference numbers used in determining the FHR and are labeled bpm. The distance between any two darker lines is 30 bpm; therefore, the distance between any two lighter lines is 10 bpm.
every two darker lines (Fig. 7.15). There is a horizontal column of numbers ranging from 30 to 240. These are reference numbers used in determining the FHR and are labeled bpm. The distance between any two darker lines is 30 bpm; therefore, the distance between any two lighter lines is 10 bpm.
 FIGURE 7.13 Strip graph monitor paper provides sections for tracing fetal heart rate and uterine activity. |
 FIGURE 7.14 Division of fetal heart rate section into time intervals. |
 FIGURE 7.15 Fetal heart rate in beats per minute (bpm). |
 FIGURE 7.16 Division of uterine activity section into time intervals. |
The contraction or uterine activity (lower) section of the graph is divided vertically by dark lines, with five light, vertical lines between every two dark lines (Fig. 7.16). The time interval between any two dark lines is 1 minute; therefore, the time interval between any two light lines is 10 seconds. This portion of the graph is also divided horizontally by dark lines, with five light, horizontal lines between every two dark lines (Fig. 7.17). The numbers ranging from 0 to 100 in the horizontal column are reference numbers that are used to determine the intensity of contractions when a pressure catheter is used; they are labeled mm Hg. The abbreviation UA stands for “uterine activity.”
Note that with the integration of electronic health records and perinatal data systems, many clinical systems no longer utilize paper tracings and clinicians read FHR tracings from a computer screen, tablet, or phone. The graphic representations still apply, and the parameters for
evaluation horizontally (time, in seconds and minutes) and vertically (range, in bpm or mm Hg) are unchanged. All FHR tracings are interpreted based on visual assessment, whether on paper or electronic screen.
evaluation horizontally (time, in seconds and minutes) and vertically (range, in bpm or mm Hg) are unchanged. All FHR tracings are interpreted based on visual assessment, whether on paper or electronic screen.
 FIGURE 7.17 Uterine activity in millimeters of mercury (mm Hg). |
Summary
Intrapartum fetal monitoring may be accomplished by IA, EFM, or a combination of both. Data regarding which modality is superior for which patients is limited by a number of deficiencies with the research to date, including lack of standardization and sample size. IA is a reasonable choice for low-risk women having uncomplicated labors, while EFM is recommended for women with risk factors or those who develop intrapartum complications. All clinicians should be familiar with the benefits and disadvantages of both methods, as well as the equipment used for each and the parameters for the evaluation of the information obtained, which for IA is primarily auditory and for EFM is both auditory and visual. In the next section, clinicians will review standardized definitions for the evaluation of EFM findings and uterine activity.
Part 2 NICHD Definitions
In 1997, the National Institute of Child Health and Development (NICHD) of the National Institutes of Health gathered a panel of experts to look at some of the issues related to EFM. This group of experts proposed detailed, quantitative, and standardized definitions of FHR patterns.14 These standardized definitions became known as the “NICHD definitions,” and by 2006, all professional organizations had adopted or endorsed the use of the NICHD definitions. In 2008, a second panel of experts convened by the NICHD reaffirmed the 1997 terminology and provided additional information on uterine activity as well as a category system for classification of FHR tracings.15 Part 2 of this module provides an overview of the current NICHD definitions and categories, as well as standardized definitions for uterine activity terminology.
Fetal Heart Rate Components
FHR Baseline
The FHR baseline has two components, the baseline rate and the variability of the baseline. The baseline FHR is defined as the approximate mean FHR rounded to increments of 5 bpm during a 10-minute segment, excluding:
Periodic and episodic changes, such as FHR accelerations or decelerations
Periods of marked variability
Any segments of the FHR tracing that differ 25 bpm or more
In the 10-minute segment, the minimum baseline duration must be at least 2 minutes (Fig. 7.18). The 2-minute minimum does not need to be contiguous. If there are less than 2 minutes of identifiable baseline, the baseline is considered indeterminate. In these cases, clinicians may need to assess additional portions of the FHR tracing to establish baseline rate. Baseline FHR is charted as a single number, not a range, and is always rounded to the nearest 5 bpm. Contrary to prior practices, the current definitions of FHR baseline does not require that baseline be read between contractions, rather it is assessed only by evaluation of the FHR portion of the monitor tracing.
Summary Terms for Baseline Fetal Heart Rate
Normal FHR baseline ranges between 110 and 160 bpm, regardless of gestational age
Tachycardia is an FHR baseline of greater than 160 bpm, regardless of gestational age
Bradycardia is an FHR baseline of less than 100 bpm, regardless of gestational age
FHR Variability
The second component of FHR baseline is variability. FHR variability is defined as fluctuations in the baseline that are irregular in amplitude and frequency. Variability is quantified by the amplitude of peak to trough, in one of four ways:
Absent—fluctuations are undetectable
Minimal—fluctuations greater than undetectable but less than or equal to 5 bpm
Moderate—fluctuations are in the range of 6 to 25 bpm
Marked—fluctuations are greater than 25 bpm (Fig. 7.19)
It is important to note that variability is a component of baseline, as in the past some clinicians have mistakenly identified irregularity within the base of an FHR deceleration as variability.
The NICHD makes it clear that secondary characteristics of variable decelerations, such as irregularity with a deceleration, have no known clinical significance based on the current evidence.15 Research completed following the 2008 NICHD Workshop, evaluating atypical characteristics of decelerations, has confirmed that when evaluating FHR decelerations, atypical findings should not be considered clinically significant.16 This means that when clinicians evaluate FHR variability they must do so only in the context of variability as a component of the identifiable FHR baseline.
The NICHD makes it clear that secondary characteristics of variable decelerations, such as irregularity with a deceleration, have no known clinical significance based on the current evidence.15 Research completed following the 2008 NICHD Workshop, evaluating atypical characteristics of decelerations, has confirmed that when evaluating FHR decelerations, atypical findings should not be considered clinically significant.16 This means that when clinicians evaluate FHR variability they must do so only in the context of variability as a component of the identifiable FHR baseline.
 FIGURE 7.18 Baseline fetal heart rate. (Courtesy PRMES, LLC.) |
Sinusoidal FHR Pattern
A sinusoidal FHR pattern is a rare FHR pattern that is defined by the NICHD as having the following visually apparent attributes15:
Smooth, visually apparent, sine wave–like undulating pattern in FHR baseline
Cycle frequency of 3 to 5 per minute
Persistence for 20 minutes or more
 FIGURE 7.19 Absent, minimal, moderate, and marked variability. (Courtesy PRMES, LLC.) |
 FIGURE 7.20 Sinusoidal pattern. (Courtesy PRMES, LLC.) |
Sinusoidal patterns are characterized by smooth, sine waves that are regular in frequency and amplitude (Fig. 7.20). The sine waves should not be mistaken for variability. The pattern may be intermittent or continuous. Sinusoidal patterns have been seen in cases of fetal anemia, historically often related to Rh sensitization.13 It has been suggested that intermittent sinusoidal baseline rate may be an early indicator of impending fetal compromise.17 Because of both the rarity of the pattern and the correlation to potential fetal compromise, physician evaluation of the FHR tracing is recommended if a sinusoidal FHR tracing is suspected.
Medication Effect
A sinusoidal-like pattern may be seen following narcotic administration (Fig. 7.21). The appearance is similar to a true sinusoidal, but the amplitude is often less, and the pattern is transitory, resolving as the medication clears the maternal system. In the past, clinicians have used the term “pseudosinusoidal” to describe this medication effect on FHR, but this is not a term defined by the NICHD and is probably best avoided. Clinicians should use considerable clinical context and history of medication administration to determine whether an FHR pattern is related to medications administered to the mother or represents a true sinusoidal pattern.
 FIGURE 7.21 Medication effect, not to be confused with a sinusoidal baseline. (Courtesy PRMES, LLC.) |
Periodic and Episodic Changes
FHR changes, which include both accelerations and decelerations, may be periodic or episodic in nature. Periodic changes are those that occur in association with a uterine contraction. Episodic patterns are those that occur randomly, unassociated with uterine contractions. By definition, late and early decelerations can only be periodic, as they require an association with a uterine contraction to be labeled as early or late. Accelerations, variable decelerations, and prolonged decelerations can be either episodic or periodic, as they can occur with or without an associated uterine contraction.
Accelerations
Accelerations are the most common type of periodic heart rate change. They are defined as a visually apparent abrupt increase in FHR (onset of acceleration to peak in less than 30 seconds) (Fig. 7.22). The peak of the acceleration is 15 bpm above the most recently determined baseline and the acceleration duration (onset to offset) is at least 15 seconds. Before 32 weeks’ gestation, a peak of 10 bpm above the baseline and a duration of 10 seconds will satisfy the criteria for an acceleration.15 Accelerations may occur spontaneously or in response to fetal movement, maternal movement, acoustic stimulation, fetal scalp stimulation, or contractions. Prolonged accelerations are those with a duration of 2 minutes or longer but less than 10 minutes. After a duration of 10 minutes, it is not considered an acceleration but rather a change in the baseline rate.
 FIGURE 7.22 Fetal heart rate acceleration. |
Early Deceleration
An early deceleration is defined as a visually apparent, gradual decrease (onset of deceleration to nadir greater than or equal to 30 seconds) and return to baseline associated with a contraction.15 The onset, nadir, and return to baseline of an early deceleration correspond with the beginning, peak, and end of a uterine contraction (Fig. 7.23). Because the definition of an early deceleration is dependent upon the deceleration’s relationship to an associated uterine contraction, early decelerations can only be periodic.
Late Deceleration
An late deceleration is defined as a visually apparent, gradual decrease (onset of deceleration to nadir greater than or equal to 30 seconds) and return to baseline associated with a contraction.15
However, in contrast to the aforementioned early deceleration, the onset of the late deceleration is delayed, beginning after the onset of the contraction, with the nadir (lowest point) occurring after the peak of the contraction, and return to baseline generally following the offset of the contraction (Fig. 7.24). Because the definition of a late deceleration is dependent upon the deceleration’s relationship to an associated uterine contraction, like early decelerations late decelerations can only be periodic.
However, in contrast to the aforementioned early deceleration, the onset of the late deceleration is delayed, beginning after the onset of the contraction, with the nadir (lowest point) occurring after the peak of the contraction, and return to baseline generally following the offset of the contraction (Fig. 7.24). Because the definition of a late deceleration is dependent upon the deceleration’s relationship to an associated uterine contraction, like early decelerations late decelerations can only be periodic.
 FIGURE 7.23 Early deceleration. (From Miller, L. A., Miller, D. A., & Tucker, S. M. (2013). Pocket guide to fetal monitoring: A multidisciplinary approach (7th ed.) St. Louis, MO: Mosby.) |
 FIGURE 7.24 Late deceleration. (Courtesy PRMES, LLC.) |
Variable Deceleration
A variable deceleration is defined as a visually apparent, abrupt decrease (onset of deceleration to nadir less than 30 seconds) and return to baseline associated with a contraction.15 The decrease in FHR from onset to nadir must be at least 15 bpm, and the duration (onset to offset) of the deceleration must be at least 15 seconds, but less than 2 minutes (Fig. 7.25). A variable deceleration may occur periodically (related to a contraction) or episodically (spontaneous, not associated with a contraction).
 FIGURE 7.25 Variable deceleration. (Courtesy PRMES, LLC.) |
Prolonged Deceleration
A prolonged deceleration is defined as a visually apparent deceleration from the FHR baseline that may be abrupt or gradual in onset.15 The decrease in FHR from onset to nadir must be at least 15 bpm, and the duration (onset to offset) of the deceleration must be 2 minutes or longer, but less than 10 minutes (Fig. 7.26). Following a duration of 10 minutes, the prolonged deceleration would likely reflect a baseline change rather than a deceleration. A prolonged deceleration may occur periodically (related to a contraction) or episodically (spontaneous, not associated with a contraction). They are often seen immediately prior to delivery during the final expulsive efforts of the mother.
FHR Categories
The 2008 NICHD workshop report introduced a three-tiered system for the categorization of FHR tracings in the intrapartum period.15 These summary terms have limited value in daily
clinical practice, but are important as an alternative to the vague and nonspecific terms (such as “reassuring” and nonreassuring”) that many clinicians have utilized in the past when attempting to summarize FHR tracing characteristics. There are three categories:
clinical practice, but are important as an alternative to the vague and nonspecific terms (such as “reassuring” and nonreassuring”) that many clinicians have utilized in the past when attempting to summarize FHR tracing characteristics. There are three categories:
 FIGURE 7.26 Prolonged deceleration (Courtesy PRMES, LLC). |
Category I, or normal, requires a normal baseline rate, moderate variability of the FHR baseline, and may include early decelerations. A category I tracing is considered “strongly predictive of normal fetal acid-base status at the time of observation.”15
Category II, or indeterminate, includes all FHR tracings that do not qualify as either category I or category III. These tracings represent the majority (80% or more) of FHR tracings that will be seen during labor.6,18
Category III, or abnormal, includes only four FHR tracings:
Absent variability with recurrent late decelerations
Absent variability with recurrent variable decelerations
Absent variability with bradycardia
Sinusoidal pattern
Category III tracings are considered predictive of abnormal fetal acid–base status at the time they are seen,15 but the high false-positive rate of EFM means that even when delivered following a category III tracing, less than 50% will actually exhibit metabolic acidemia in umbilical cord blood, and even in those with abnormal cord gases at birth, not all will go on to develop any long-term morbidity.7 Thus, “predictive of” is not equivalent to “diagnostic for” when discussing fetal acid–base status or neurologic outcome in relation to EFM tracings in category III. Nonetheless, as will be discussed in interpretation and management, category III tracings require prompt intervention and, if unresolved with conservative corrective measures, expeditious delivery with planned neonatal support.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
