Fetal Heart Rate Monitoring

Author - Kimberly A. Pickett, RN, BSN, CEN

Abstract

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hile the benefits of fetal monitoring are apparent, there are also risks. Proper evaluation and interpretation of data gathered can provide means for assessing the unborn fetus, identifying potential problems and providing stabilization for the patient and fetus, especially in the transport environment. On the downside, data can be misinterpreted by untrained clinicians, unnecessary interventions such as c-sections may be expedited and the information can be used against a healthcare team in legal proceedings.

Objectives

1. Briefly discuss options for fetal monitoring

2. Identify various fetal heart rate patterns and their significance

3. Develop a systematic approach to reading a fetal heart beat tracing

4. Determine if the fetal heart tracing is reassuring, non-reassuring or ominous

5. Discuss appropriate interventions in the presence of non-reassuring fetal heart rates

This course has been approved for one contact hour by the Florida Board of Nursing provider number NCE3510.

Introduction

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here are several ways to provide fetal monitoring. The first two are quite simple, while the others require more advanced equipment which is often not feasible in a transport environment. Auscultation involves using a Doppler to listen to the fetal heart beat. In addition, uterine palpation is helpful in determining the intensity of contractions. These two methods can be easily implemented and provide effective means of evaluation and monitoring.

Other types of monitoring include external and internal. External monitoring consists of using ultrasound to monitor the fetal heart rate and a tocodynamometer (“toco” – labor; “dyna” – power; “meter” – measure) which monitors contraction patterns. An internal method called FECG (Fetal ElectroCardioGram) or FSE (Fetal Scalp Electrode) monitors fetal heart rate. Since it is a true representation of the heart rate, it is recommended if there are any questions regarding the presence of long-term or short-term variability. If a patient has intact membranes or is preterm, this type of monitoring is contraindicated. The same can be said for the Intrauterine Pressure Catheter (IUPC) which monitors the contraction pattern and true contraction strength.

Just like evaluating an EKG for a cardiac patient, a fetal heart tracing should be interpreted using a systematic approach. Reviewing a patient’s EKG prior to transport is considered common practice. Reviewing a fetal heart tracing should be considered just as important. Granted, not all patients will be at facilities in which electronic monitoring is available, but when available, being able to interpret the patterns will aid you in the preparation and care of the patient during transport. In some cases, interpretation may also lead you to reconsider the safety of transporting the patient.

When electronic continuous fetal monitoring is not available, the transport team will need to rely on a Doppler and palpation. It is important to explain to your patient that she will need to make you aware of her contractions and any other changes she experiences. During a contraction, you will palpate the uterus at the top of the fundus. Contractions should be recorded including intensity, duration, and regularity. One way to determine the intensity of a contraction is by comparing the firmness of the uterus to areas on your face. For example, your cheek could be considered mild, the tip of your nose as moderate, and your forehead as strong.

When at a facility without electronic fetal monitoring, get a baseline fetal heart rate by using your Doppler prior to transport. Afterwards, FHR should be monitored at least every 15 minutes in the absence of contractions or other factors. However, if contractions are active, FHR should be auscultated during the contraction and for 30 – 60 seconds after to identify fetal response.

Developing a System

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he following is a systematic approach to reading an electronic fetal heart rate tracing as suggested by Sweha, Hacker and Nuovo (1999).

1.   Evaluate if the recording is continuous and adequate for interpretation.

2.   Identify the type of monitor used – internal vs. external.

3.   Identify baseline fetal heart rate and presence of variability, both long-term and short-term.

4.   Determine whether accelerations or decelerations from the baseline occur.

5.   Identify the pattern of uterine contractions, including regularity, rate, intensity, duration, and baseline tone between contractions.

6.   Correlate accelerations and decelerations with uterine contractions.

7.   If possible, identify changes in fetal heart rate tracing.

8.   Conclude whether the FHR tracing is reassuring, non-reassuring or ominous.

9.   Provide interventions as indicated by clinical scenario and interpretation of FHR.

10.   Document, document, document.

Determining the Baseline

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egin by determining the baseline heart rate over a ten minute period. A tracing is recorded on scaled paper with one small square = 10 seconds and one large square = 60 seconds. The baseline fetal heart rate is the heart rate range that occurs between contractions. The heart rate should be rounded to the nearest 5 beats per minute (bpm) increment, excluding any marked FHR variability, periodic or episodic changes and segments of baseline that differ by 25 bpm. The normal average baseline fetal heart rate in the third trimester is between 120 – 160 bpm. Slow heart rates are common from head compression during the second stage of labor. Other causes can include congenital heart block, serious fetal compromise, severe pyelonephritis and maternal hypothermia.

A typical tracing from a patient with a tocodynameter and fetal heart monitor in place

Fetal Bradycardia

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ild fetal bradycardia is determined if heart rate is less than 120 bpm and lasts 15 minutes or longer. However, a FHR of 110-119 bpm in the absence of other changes does not usually mean fetal compromise. Moderate bradycardia is a FHR of 80 – 100 bpm, and severe bradycardia is 80 bpm lasting 3 minutes or longer. A baseline change occurs with the increase or decrease in heart rate lasting longer than 10 minutes.

Fetal bradycardia can result from several factors. Medications such as narcotics can cause slower fetal heart rates by preventing receptor sites in the fetal heart muscle from accepting epinephrine which works to increase the heart rate. Epidurals cause vasodilation which can lead to maternal hypotension. The anesthetic agents used in the epidurals can cause bradycardia indirectly due to a reflex mechanism or as a result of hypotension. Administration of synthetic oxytocin (Pitocin) may lead to fetal bradycardia by causing a hyperstimulation of the uterine muscles which leads to fetal hypoxia. Maternal hypotension, or supine hypotension syndrome, results in decreased maternal blood pressure. A prolapsed cord or prolonged compression of the umbilical cord can activate the fetus’ regulatory mechanism causing a stimulation of the vagal center (part of the parasympathetic nervous system) which results in bradycardia. It is important to remember that bradycardia is a late sign of fetal hypoxia (a continued lack of oxygen). The heart rate slows in response to a depression of the heart muscle activity caused by the continued decrease in needed oxygen. Seeking immediate assistance is imperative since this is a fetal emergency.

A tracing showing fetal bradycardia. Notice the heart rate is below the acceptable range of 120 to 160 bpm for an extended period of time.

Fetal Tachycardia

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etal tachycardia is noted when the heart rate exceeds 160 bpm. It is an early sign of hypoxia. Like bradycardia, it can be caused by many factors. Medications to stop or slow premature labor such as Terbutaline have a stimulating effect on the fetal heart. Maternal anxiety causes epinephrine to be released into the mother’s blood stream which crosses the placenta to the fetus resulting in an increased heart rate. In the presence of maternal fever, both mother’s and baby’s metabolism increases causing an increased heart rate. Prematurity can result in an increased heart rate secondary to an immature nervous system. Tachycardia may also be a sign of fetal infection. Fetal movement and/or stimulation can lead to tachycardia, but in this situation it is considered benign.

A tracing showing fetal bradycardia. Notice the heart rate is below the acceptable range of 120 to 160 bpm for an extended period of time.

Variability

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he next step is to determine the variability. The FHR is under constant variation from the baseline. Variability is a reflection of a healthy nervous system and is a good indicator of fetal well-being. Beat to beat variability is the ability of the fetal heart to respond to external stimuli through a well balanced sympathetic and parasympathetic nervous system.

After 32 weeks gestation, variability should be normal. Prematurity decreases variability, so there is little fluctuation before 28 weeks. Other causes of decreased variability are fetal hypoxia and acidosis, congenital heart defects and fetal tachycardia. Beat-to-beat or short-term variability is the oscillation of the FHR around the baseline in amplitude of 5 to 10 bpm. It is described as either present or absent, and it is most accurately recorded by an internal spiral electrode. Long-term variability is the fluctuations or oscillations in the fetal heart rate over one minute. Long-term variability is mostly controlled by the autonomic nervous system. Clinically, loss of beat-to-beat variability is more significant than loss of long-term variability and may be ominous.

Long-Term Variability (LTV) is described as being:

Absent = 0 – 2 BPM

Minimal = 3 – 5 BPM

Average = 6 – 10 BPM

Moderate = 10 – 25 BPM

Marked = > 25 BPM

Reduced Variability - Notice that the heart rate stays between 150 and 160 bpm, a range of less than 10 bpm.

A normal, healthy fetus should exhibit average to moderate variability. A decrease in variability can be seen with fetal sleep, maternal medication administration or fetal anomalies. Persistent minimal or absent variability may be a sign of inadequate fetal oxygenation, so when the duration lasts longer than a fetal sleep cycle which is 20-40 minutes, further evaluation is indicated. It should be considered especially ominous if there are persistent late decelerations or repetitive, severe, prolonged variable decelerations.

A sinusoidal pattern is a smooth, undulating pattern, lasting at least 10 minutes with a fixed period of three to five cycles per minute and an amplitude of 5 -15 BPM. A true sinusoidal pattern is rare but ominous with high rates of fetal morbidity and mortality (Sweha & Nuovo, 1999). Fetal activity may be minimal or absent, and FHR accelerations are lacking. Also, there is no beat-to-beat short-term variability. “Oscillation of 25 bpm or more has significantly greater perinatal mortality as, compared to, oscillation less than 25 bpm - 67% vs 1% (Katz, 1994). This pattern is associated with Rh isoimmunization, severe anemia, and occasionally, asphyxiation.

Sinusoidal Pattern

The pseudo-sinusoidal FHR pattern appears very similar to the sinusoidal pattern; however, this pattern shows less regularity in the shape and amplitude of the variability waves and the presence of beat-to-beat variability. This type of pattern is benign and transient, and can occur in the presence of narcotics.

Pseudo-sinusoidal Pattern

Another type of fetal heart rate is a saltatory pattern. It is rapidly occurring couples of acceleration and deceleration causing relatively large oscillations of the baseline fetal heart rate. This pattern is usually caused by acute hypoxia or mechanical compression of the umbilical cord. It is considered a non-reassuring pattern, but it is not usually an indication for immediate delivery.

Saltatory Pattern - Saltatory means marked by dancing or jumping and is an appropriate term for the erratic pattern displayed.

Accelerations

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he presence of accelerations is the third indicator to assess. Accelerations are transient increases in the fetal heart rate caused by fetal movement. They are good indications of fetal well-being and adequate oxygen reserve. Accelerations often accompany contractions as a result of fetal movement in response to the pressure of contracting uterine muscles. During an acceleration, the FHR increases by more than 15 BPM for more than 15 seconds (the 15 x15 rule). In the normal mature fetus, accelerations can be triggered by fetal body motion, sounds, and other stimuli. They are considered benign and are a reassuring sign that shows fetal responsiveness and the integrity of mechanisms controlling the heart.

Accelerations - Notice the significant heart rate increase, especiialy around the contractions.

Decelerations

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here are three types of decelerations to consider when interpreting a fetal heart tracing. The first is an early deceleration which is defined as a deceleration pattern that matches the contraction with the peak, or nadir, of the deceleration occurring at the peak of the contraction. It appears almost as a mirror image of the contractions. This type of deceleration is normal and common, occurring secondary to head compression during uterine contraction. Early decelerations are often seen in active labor with cervical dilation of 4 -7 cm. Typically they do not require any treatment other than continued observation and reassessment.

Early Decelerations - Notice the decrease in the fetal heart rate, starting at about the same time as the onset of the contraction.

A late deceleration is a decrease is FHR from baseline that usually begins at the middle of a contraction and remains below baseline until after the contraction is complete. The FHR will only improve after the contraction has ended.

Late Deceleration with Absent Variability - Notice the decrease in the fetal heart rate only begins to decline after the contraction peaks.

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ow low the FHR goes and the length of time it takes for the FHR to recover determines if the decelerations are mild or severe. Late decelerations are the most ominous fetal heart rate pattern. They are caused by reduced or lack of blood flow to the uterus and placenta during a contraction. Late decelerations are associated with uteroplacental insufficiency and are a consequence of hypoxia and metabolic abnormalities. Uteroplacental insufficiency can result from pregnancy-induced hypertension, diabetes, cardiovascular or kidney disease, choriamnionitis, smoking and a fetus that is past maturity. It can also be caused by a decrease in placental perfusion in placental abruption or previa, uterine hypertonus and hypotension.

Variable decelerations are a common type of FHR decelerations occurring with up to 80% of fetuses. They can occur at any time during a contraction; the shape can vary, and is frequently V-shaped or W-shaped. They are characterized by a frequently short acceleration followed by a rapid deceleration for some seconds, then a rapid rise and a short acceleration before returning to baseline. The significance of these decelerations are determined by how low the FHR drops, and how long the episode lasts. They are classified as severe if they last more than 60 seconds or lead to FHR less than 90 BPM.

Variable Decelerations - Notice that the decelerations are not related to the contraction, beginning well before the contraction even begins.

Cord compression is usually responsible for variable decelerations, and it can occur in several circumstances. They are common with oligohydramnios, nuchal cord or short cord. When the membranes rupture, there is less fluid to cushion the cord which can also lead to cord compression. In regards to treatment, maternal position change may be beneficial. . [Severe Decels] Severe Variable Decelerations

Reassuring vs. Non-Reassuring Patterns

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etal heart rate patterns can be interpreted as reassuring, non-reassuring or ominous. While reassuring patterns are associated with good fetal outcome, non-reassuring patterns do not. The table below lists examples of non-reassuring and ominous patterns.

Interventions

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n the presence of a non-reassuring fetal heart pattern, the following interventions are recommended, and can be accomplished during transport. These interventions should also be initiated in the case of ominous patterns, while the receiving facility is notified so they can make preparations for possible immediate delivery. A formula for remembering interventions is “LOCK.”