From Macones GA, Hankins GD, Spong CY, et al: The 2008 National Institute of Child Health and Human Development Workshop Report on Electronic Fetal Monitoring: update on definitions, interpretation, and research guidelines, J Obstet Gynecol Neonatal Nurs 37(5):510–515, 2008.

Uterine Activity

Table 15-1 describes normal uterine activity (UA) during labor.

TABLE 15-1

NORMAL UTERINE ACTIVITY DURING LABOR

CHARACTERISTIC	DESCRIPTION
Frequency	Contraction frequency overall generally ranges from two to five per 10 minutes during labor, with lower frequencies seen in first stage of labor and higher frequencies (up to five contractions in 10 minutes) seen during second stage of labor.
Duration	Contraction duration remains fairly stable throughout first and second stages, ranging from 45-80 seconds, not generally exceeding 90 seconds.
Strength	Uterine contractions generally range from peaking at 40-70 mm Hg in first stage of labor to over 80 mm Hg in second stage. Contractions palpated as “mild” would likely peak at less than 50 mm Hg if measured internally, whereas contractions palpated as “moderate” or greater would likely peak at 50 mm Hg or greater if measured internally.
Resting tone	Average resting tone during labor is 10 mm Hg; if using palpation, should palpate as “soft” (i.e., easily indented, no palpable resistance).
Relaxation time	Relaxation time is commonly 60 seconds or more in first stage and 45 seconds or more in second stage.
Montevideo units (MVUs)	MVUs usually range from 100-250 in first stage; may rise to 300-400 in the second stage. Contraction intensities of 40 mm Hg or more and MVUs of 80-120 are generally sufficient to initiate spontaneous labor. MVUs are used only with internal monitoring of contractions.

Data from Macones GA, Hankins GD, Spong CY, et al: The 2008 National Institute of Child Health and Human Development Workshop Report on Electronic Fetal Monitoring: update on definitions, interpretation, and research guidelines, J Obstet Gynecol Neonatal Nurs 37(5):510–515, 2008; Miller LA, Miller DA, Tucker SM: Mosby’s pocket guide to fetal monitoring: a multidisciplinary approach, ed 7, St Louis, 2013, Mosby.

Fetal Compromise

The goals of intrapartum FHR monitoring are to identify and differentiate the normal (reassuring) patterns from the abnormal (nonreassuring) patterns, which can indicate fetal compromise. Although the 2008 National Institute of Child Health and Human Development workshop (Macones, Hankins, Spong, et al., 2008) and the ACOG (2009) both recommend use of the terms normal and abnormal to describe FHR tracings, the terms reassuring and nonreassuring are still frequently used clinically.

Abnormal FHR patterns are those associated with fetal hypoxemia, which is a deficiency of oxygen in the arterial blood. If uncorrected, hypoxemia can deteriorate to severe fetal hypoxia, an inadequate supply of oxygen at the cellular level that can cause metabolic acidosis. The term asphyxia is used when fetal hypoxia results in metabolic acidosis (Garite, 2012). See Box 15-1 for examples of abnormal (category III) FHR tracings.

Monitoring Techniques

The ideal method of fetal assessment during labor continues to be debated. Research findings support the use of both IA of the FHR and EFM (Gilbert, 2011). Although IA is a high-touch, low-technology method of assessing fetal status during labor that places fewer restrictions on maternal activity, more than 85% of laboring women in the United States are monitored electronically for at least part of their labor (ACOG, 2009; Miller, Miller, and Tucker, 2013). The continued use of EFM in place of IA is thought to be because of concerns about liability and the increased nurse-patient ratio required with IA. Because all surveillance methods, including EFM, have limitations, some believe that the evidence supports a return to the use of IA for low risk laboring women (ACOG, 2009; Miller, Miller, and Tucker, 2013).

Intermittent Auscultation

Intermittent auscultation involves listening to fetal heart sounds at periodic intervals to assess the FHR. IA of the fetal heart can be performed with a Pinard stethoscope (Fig. 15-1), Doppler ultrasound (Fig. 15-2, A), an ultrasound stethoscope (see Fig. 15-2, B), or a DeLee-Hillis fetoscope (see Fig. 15-2, C). Doppler ultrasound and ultrasound stethoscopes transmit ultra high–frequency sound waves, reflecting movement of the fetal heart, and convert these sounds into an electronic signal that can be counted. The fetoscope is applied to the listener’s forehead because bone conduction amplifies the fetal heart sounds for counting. Box 15-2 describes how to perform IA.

Box 15-2

Procedure for Intermittent Auscultation of the Fetal Heart Rate

1. Palpate maternal abdomen to identify fetal presentation and position.

2. Apply ultrasonic gel to device if using Doppler ultrasound. Place listening device (see Figs. 15-1 and 15-2) over area of maximal intensity and clarity of fetal heart sounds to obtain clearest and loudest sound, which is easiest to count. This location is usually over the fetal back. If using fetoscope, firm pressure may be needed.

3. Count maternal radial pulse while listening to FHR to differentiate it from fetal rate.

4. Palpate abdomen for presence or absence of UA to count FHR between contractions.

5. Count FHR for 30 to 60 seconds after a uterine contraction to identify auscultated baseline rate and changes (increases or decreases) in it.

6. Auscultate FHR before, during, and after contraction to identify FHR during the contraction or as a response to the contraction and to assess for absence or presence of increases or decreases in FHR.

7. When distinct discrepancies in FHR are noted during listening periods, auscultate for longer period during, after, and between contractions to identify significant changes that may indicate need for another mode of FHR monitoring.

FHR, Fetal heart rate; UA, uterine activity.

From Miller LA, Miller DA, Tucker SM: Mosby’s pocket guide to fetal monitoring: a multidisciplinary approach, ed 7, St Louis, 2013, Mosby.

IA is easy to use, inexpensive, and less invasive than EFM. It is often more comfortable for the woman and gives her more freedom of movement. Other care measures such as ambulation and the use of baths or showers are easier to carry out when IA is used. However, it may be difficult to perform transabdominally in women who are obese. A transvaginal fetal Doppler probe is now available. It provides closer proximity to the uterus, making it easier to auscultate the FHR when the woman is obese or early in gestation (Miller, Miller, and Tucker, 2013). Because IA is intermittent, significant events may occur during a time when the FHR is not being auscultated. In addition, IA does not provide a permanent documented visual record of the FHR and cannot be used to assess visual patterns of the FHR variability or periodic changes (Miller, Miller, and Tucker, 2013). By using IA the nurse can assess the baseline FHR, rhythm, and increases and decreases from baseline.

The American College of Nurse-Midwives (ACNM) reviewed references from the United States, Great Britain, and Canada regarding the recommended frequency of IA in low risk women and found consistent recommendations for every 15 minutes in the active phase of the first stage of labor and every 5 minutes in the second stage of labor (Miller, Miller, and Tucker, 2013). The ACOG (2009) agrees that these time frames are acceptable for IA in low risk women. The Association of Women’s Health, Obstetric and Neonatal Nurses recommends different IA frequencies: every hour in the latent phase of first-stage labor, every 30 minutes in the active phase of first-stage labor, and every 15 minutes in the second stage of labor (AWHONN, 2009). However, the optimal frequency for IA in low risk women during labor has not been determined (Nageotte and Gilstrap, 2009).

Nursing Alert

When the FHR is auscultated and documented, it is inappropriate to use the descriptive terms associated with EFM (e.g., moderate variability, variable deceleration) because most of the terms are visual descriptions of the patterns produced on the monitor tracing. However, terms that are numerically defined such as bradycardia and tachycardia can be used. When FHR is auscultated, it should be described as a baseline number or range and as having a regular or irregular rhythm. The presence or absence of accelerations or decelerations both during and after contractions should also be noted (AWHONN, 2009; Miller, Miller, and Tucker, 2013).

Every effort should be made to use the method of fetal assessment the woman desires if possible. However, auscultation of the FHR in accordance with the frequency guidelines suggested earlier may be difficult in today’s busy labor and birth units. When used as the primary method of fetal assessment, auscultation requires a one-to-one nurse-to-patient staffing ratio. If acuity and census change so auscultation standards are no longer met, the nurse must inform the physician or nurse-midwife that continuous EFM will be used until staffing can be arranged to meet the standards.

The woman can become anxious if the examiner cannot readily count the fetal heartbeats. It often takes time for the inexperienced listener to locate the heartbeat and find the area of maximal intensity. To allay the mother’s concerns, she can be told that the nurse is “finding the spot where the sounds are loudest.” If it takes considerable time to locate the fetal heartbeats, the examiner can reassure the mother by offering her an opportunity to listen to them. If the examiner cannot locate the fetal heartbeat, assistance should be requested. In some cases ultrasound can be used to help locate the fetal heartbeat. Seeing the FHR on the ultrasound screen is reassuring to the mother if there was initial difficulty in locating the best area for auscultation.

When using IA, UA is assessed by palpation. The examiner should keep his or her fingertips placed over the fundus before, during, and after contractions. The contraction intensity is usually described as mild, moderate, or strong. The contraction duration is measured in seconds, from the beginning to the end of the contraction. The frequency of contractions is measured in minutes, from the beginning of one contraction to the beginning of the next. The examiner should keep his or her hand on the fundus after the contraction is over to evaluate uterine resting tone or relaxation between contractions. Resting tone between contractions is usually described as soft or relaxed (AWHONN, 2009).

Accurate and complete documentation of fetal status and UA is especially important when IA and palpation are being used because no paper tracing record or computer storage of these assessments is provided as is the case with continuous EFM. Labor flow records or computer charting systems that prompt notations of all assessments are useful for ensuring such comprehensive documentation.

Electronic Fetal Monitoring

The purpose of EFM is the ongoing assessment of fetal oxygenation. FHR tracings are analyzed for characteristic patterns that suggest fetal hypoxic events and metabolic acidosis during labor. When hypoxia or metabolic acidosis is suspected in labor, interventions to resolve the problem can be implemented in a timely manner before permanent damage or death occurs (Garite, 2012). The two modes of EFM are the external mode, which uses external transducers placed on the maternal abdomen to assess FHR and UA; and the internal mode, which uses a spiral electrode applied to the fetal presenting part to assess the FHR and an intrauterine pressure catheter (IUPC) to assess UA and uterine resting tone. The differences between the external and internal modes of EFM are summarized in Table 15-2.

TABLE 15-2

EXTERNAL AND INTERNAL MODES OF MONITORING

EXTERNAL MODE	INTERNAL MODE
Fetal Heart Rate
Ultrasound transducer: High-frequency sound waves reflect mechanical action of fetal heart; noninvasive; does not require rupture of membranes or cervical dilation; used during both antepartum and intrapartum periods	Spiral electrode: Converts fetal ECG as obtained from presenting part to FHR via cardiotachometer; can be used only when membranes are ruptured and cervix is sufficiently dilated during intrapartum period; electrode penetrates into fetal presenting part by 1.5 mm and must be attached securely to ensure good signal
Uterine Activity
Tocotransducer: Monitors frequency and duration of contractions by means of pressure-sensing device applied to maternal abdomen; used during both antepartum and intrapartum periods.	Intrauterine pressure catheter (IUPC): Monitors frequency, duration, and intensity of contractions; two types of IUPCs: fluid-filled system and solid catheter; both measure intrauterine pressure at catheter tip and convert pressure into millimeters of mercury on uterine activity panel of strip chart; both can be used only when membranes are ruptured and cervix is sufficiently dilated during intrapartum period

ECG, Electrocardiogram; FHR, fetal heart rate.

External Monitoring

Separate transducers are used to monitor the FHR and UCs (Fig. 15-3). The ultrasound transducer works by reflecting high-frequency sound waves off a moving interface, in this case the fetal heart and valves. It is sometimes difficult to reproduce a continuous and precise record of the FHR because of artifact introduced by fetal and maternal movement. Maternal obesity, occiput posterior position of the fetus, and anterior attachment of the placenta can cause weak or absent signals (AWHONN, 2009). The FHR is printed on specially formatted monitor paper. The standard paper speed used in the United States is 3 cm/min. Once the area of maximal intensity of the FHR has been located, conductive gel is applied to the surface of the ultrasound transducer, and the transducer is then positioned over this area and held securely in place using an elastic belt (see Critical Thinking Case Study).

FIG 15-3 A, External noninvasive fetal monitoring with tocotransducer and ultrasound transducer. *FHR*, fetal heart rate. B, Ultrasound transducer is placed below umbilicus over area where fetal heart rate is best heard, and tocotransducer is placed on uterine fundus. (B, Courtesy Julie Perry Nelson, Loveland, CO.)

Critical Thinking Case Study

Fetal Heart Rate Recording

You are assigned to Lauren, a 29-year-old G1 P0 who is in the first stage of labor. She wonders why the fetal heart rate (FHR) is sometimes not being recorded on the monitor paper. She asks if there is “something wrong with the baby” when the FHR is not recording continuously. Based on your knowledge of how the external monitor works, you explain the lack of continuous recording of the FHR and how you plan to improve the tracing and document your observations.

1. Evidence—Is there sufficient evidence to draw any conclusions about what causes gaps in recording on the monitor paper and ways to improve the tracing?

2. Assumptions—Describe an underlying assumption about each of the following issues:

a. Efficacy of FHR monitoring in improving pregnancy outcome

b. Causes of poor quality tracings when using the external mode of FHR monitoring

c. Signs of abnormal FHR patterns

d. Causes of periodic and episodic changes in the FHR

3. What implications and priorities for nursing care can be drawn at this time?

4. Does the evidence objectively support your argument (conclusion)?

The tocotransducer (tocodynamometer) measures UA transabdominally. The device is placed over the fundus above the umbilicus and held securely in place with an elastic belt (see Fig. 15-3, B). UCs or fetal movements depress a pressure-sensitive surface on the side next to the abdomen. The tocotransducer can measure and record the frequency and approximate duration of UCs but not their intensity. This method is especially valuable for measuring UA during the first stage of labor in women with intact membranes or for antepartum testing. If the woman is obese, the tocotransducer may be unable to detect the exact frequency and duration of UA.

Because the tocotransducer of most electronic fetal monitors is designed for assessing UA in the term pregnancy, it may not be sensitive enough to detect preterm UA. When monitoring the woman in preterm labor, remember that the fundus may be located below the level of the umbilicus. The nurse may need to rely on the woman to indicate when UA is occurring and to use palpation as an additional way of assessing contraction frequency and validating the monitor tracing.

The external transducers are applied easily by the nurse but often must be repositioned as the woman or fetus changes position. The woman is asked to assume a semi-Fowler’s or lateral position. Use of external transducers confines the woman to bed or chair.

Portable telemetry monitors allow observation of the FHR and UC patterns by means of centrally located electronic display stations. These portable units permit the woman to walk around during electronic monitoring.

In 2011 an external monitor became available for use in the United States. The Monica AN24 uses abdominally obtained electronic impulses to monitor both FHR and UA (Fig. 15-4, A and B). The monitor uses five electrodes placed on the woman’s abdomen to directly monitor the electrocardiogram from the maternal and fetal hearts and the electromyogram from the uterine muscle. This information is transmitted wirelessly, via Bluetooth technology, to an interface device that allows the FHR and UA data to print or display on a standard fetal monitor (Miller, Miller, and Tucker, 2013).

FIG 15-4 A, Monica AN24 is a wireless and beltless device that can be used with existing monitors to obtain fetal heart rate via abdominal electrocardiogram (ECG). B, Electrodes placed on maternal abdomen monitor ECG from fetal and maternal heart and electromyogram (EMG) from uterine muscle. (Courtesy Monica Healthcare Ltd, Nottingham, UK.)

The Monica AN24 eliminates much of the problem caused by signal loss resulting from maternal or fetal movement or maternal obesity that often occurs with traditional external monitors. The monitor also more accurately measures the frequency, occurrence of peak, and duration of UCs than does the traditional tocotransducer, although it does not provide actual intensity measurement in millimeters of mercury (mm Hg) as an IUPC does. Other advantages of the Monica AN24 are that it eliminates the need for abdominal belts and frequent readjustment of the tocotransducer and ultrasound transducer and provides some patient mobility. The woman may move up to 50 feet away from the interface device without signal loss (Fig. 15-5, A and B). In the United States the Monica AN24 is only approved for use in pregnancies that have reached 36 completed weeks or more of gestation (Miller, Miller, and Tucker, 2013). The Monica AN24 monitor may not be readily available for use in all labor and birth settings.

FIG 15-5 A, Woman sitting on birthing ball, and B, woman ambulating, both wearing Monica AN 24. (Courtesy Monica Healthcare Ltd, Nottingham, UK.)

Internal Monitoring

The technique of continuous internal FHR or UA monitoring provides a more accurate appraisal of fetal well-being during labor than external monitoring because it is not interrupted by fetal or maternal movement or affected by maternal size (Fig. 15-6). For this type of monitoring the membranes must be ruptured, the cervix sufficiently dilated (at least 2 to 3 cm), and the presenting part low enough to allow placement of the spiral electrode or IUPC or both. Internal and external modes of monitoring may be combined (i.e., internal FHR with external UA or external FHR with internal UA) without difficulty.

FIG 15-6 Diagrammatic representation of internal invasive fetal monitoring with intrauterine pressure catheter and spiral electrode in place (membranes ruptured and cervix dilated).

Internal monitoring of the FHR is accomplished by attaching a small spiral electrode to the presenting part. For UA to be monitored internally an IUPC is introduced into the uterine cavity. The catheter has a pressure-sensitive tip that measures changes in intrauterine pressure. As the catheter is compressed during a contraction, pressure is placed on the pressure transducer. This pressure is then converted into a pressure reading in millimeters of mercury. The IUPC can objectively measure the frequency, duration, and intensity of UCs and uterine resting tone.

Because it can measure the intensity of individual UCs precisely, the IUPC can be used to evaluate the adequacy of UA for achieving progress in labor. Montevideo units (MVUs) are calculated by subtracting the baseline uterine pressure from the peak contraction pressure for each contraction that occurs in a 10-minute window and then adding together the pressures generated by each contraction that occurs during that period of time. Spontaneous labor usually begins when MVUs are between 80 and 120. Uterine activity during the first stage of normal labor rarely exceeds 250 MVUs (see Table 15-1) (Cunningham, Leveno, Bloom, et al., 2010; Miller, Miller, and Tucker, 2013).

Display

The FHR and UA are displayed on the monitor paper or computer screen, with the FHR in the upper section and UA in the lower section. Fig. 15-7 contrasts the internal and external modes of electronic monitoring. Note that each small square on the monitor paper or screen represents 10 seconds; each larger box of six squares equals 1 minute (when paper is moving through the monitor at the rate of 3 cm/min).

Fetal Heart Rate Patterns

Characteristic FHR patterns are associated with fetal and maternal physiologic processes and have been identified for many years. However, because EFM was introduced into clinical practice before consensus was reached regarding standardized terminology, variations in the description and interpretation of common FHR patterns were often great. In 1997 the National Institute of Child Health and Human Development (NICHD) published a proposed nomenclature system for EFM interpretation with standardized definitions for FHR monitoring. However, the NICHD recommendations were not widely incorporated into clinical practice until they were endorsed by the ACOG in 2005. Shortly thereafter use of the NICHD standard terminology was also endorsed by the AWHONN and the ACNM (Miller, Miller, and Tucker, 2013). All three organizations cited concerns regarding patient safety and the need for improved communication among caregivers as reasons for using standard EFM definitions in clinical practice.

In April 2008 the NICHD, the ACOG, and the Society for Maternal-Fetal Medicine partnered to sponsor another workshop to revisit the FHR definitions recommended by the NICHD in 1997. The 1997 FHR definitions were reaffirmed at this workshop. In addition, new definitions related to UA and a three-tier system of FHR pattern interpretation and categorization were recommended (see Box 15-1) (Macones, Hankins, Spong, et al., 2008).

Baseline Fetal Heart Rate

The intrinsic rhythmicity of the fetal heart, the central nervous system (CNS), and the fetal autonomic nervous system control the FHR. An increase in sympathetic response results in acceleration of the FHR, whereas an increase in parasympathetic response produces a slowing of the FHR. Usually a balanced increase of sympathetic and parasympathetic response occurs during contractions, with no observable change in the baseline FHR.

The baseline FHR is the average rate during a 10-minute segment that excludes periodic or episodic changes, periods of marked variability, and segments of the baseline that differ by more than 25 beats/min. There must be at least 2 minutes of interpretable baseline data in a 10-minute segment of tracing to determine the baseline FHR (Macones, Hankins, Spong, et al., 2008). After 10 minutes of tracing is observed, the approximate mean rate is rounded to the closest 5 beats/min interval (AWHONN, 2009). For example, if the FHR rate varies between 130 and 140 beats/min over a 10-minute period, the baseline is recorded as 135 beats/min. The normal range at term is 110 to 160 beats/min. In the preterm fetus the baseline rate is slightly higher.

Variability

Variability of the FHR can be described as irregular waves or fluctuations in the baseline FHR of two cycles per minute or greater (Macones, Hankins, Spong, et al., 2008). It is a characteristic of the baseline FHR and does not include accelerations or decelerations of the FHR. Variability is quantified in beats per minute and is measured from the peak to the trough of a single cycle. Four possible categories of variability have been identified: absent, minimal, moderate, and marked (Fig. 15-8). In the past variability was described as either long term or short term (beat to beat). However, the NICHD definitions do not distinguish between long- and short-term variability because in actual practice they are visually determined as a unit (NICHD, 1997).