# Intrapartum Fetal Heart Rate Monitoring and Interpretation

## Methods of Monitoring

### Continuous Electronic Fetal Monitoring (EFM)

Continuous electronic fetal monitoring is the standard practice in most US hospitals during labor management. External monitoring uses a Doppler ultrasound transducer placed on the maternal abdomen. It is non-invasive but may lose signal with maternal movement or obesity. Internal monitoring uses a fetal scalp electrode that records a direct ECG from the fetal scalp, providing a more reliable signal. Internal monitoring requires ruptured membranes, adequate cervical dilation, and a known presenting part. Contraindications to scalp electrode placement include maternal HIV with a high viral load, hepatitis C (relative contraindication), and face presentation.

### Intrauterine Pressure Catheter (IUPC)

An intrauterine pressure catheter measures intrauterine pressure in Montevideo units. It is useful for assessing contraction adequacy when external monitoring is unreliable. Adequate contractions are defined as 200 or more Montevideo units in a 10-minute window.

### Intermittent Auscultation (IA)

Intermittent auscultation uses a handheld Doppler or Pinard stethoscope and is an acceptable monitoring method for low-risk patients. Auscultation is performed every 15 to 30 minutes during the active first stage and every 5 to 15 minutes during the second stage. This method requires a one-to-one nursing ratio. It does not detect variability or decelerations as reliably as continuous EFM. Importantly, no difference in neonatal outcomes has been demonstrated between intermittent auscultation and continuous EFM in low-risk populations, and intermittent auscultation is associated with lower cesarean and operative delivery rates.

## NICHD Terminology and Definitions

### Baseline Fetal Heart Rate

The baseline is the average fetal heart rate over a 10-minute window, excluding accelerations, decelerations, and periods of marked variability. The normal range is 110 to 160 beats per minute. Tachycardia is defined as a baseline above 160 bpm sustained for 10 minutes or more. Causes include maternal fever, chorioamnionitis, fetal infection, maternal dehydration, beta-agonist medications, fetal anemia, compensatory fetal hypoxia, and fetal arrhythmia. Bradycardia is defined as a baseline below 110 bpm sustained for 10 minutes or more. Causes include cord compression, maternal hypotension, uterine rupture, prolonged pushing, congenital heart block, and umbilical cord prolapse.

### Baseline Variability

Baseline variability refers to fluctuations in the baseline fetal heart rate, measured from peak to trough. Absent variability means the amplitude is undetectable. Minimal variability is an amplitude of 5 bpm or less. Moderate variability, defined as an amplitude of 6 to 25 bpm, is the most reassuring finding because it reflects an intact central nervous system-cardiac axis. Marked variability is an amplitude exceeding 25 bpm. Moderate variability is the single most reassuring feature of a fetal heart rate tracing and virtually excludes ongoing fetal metabolic acidemia.

### Accelerations

An acceleration is an abrupt increase in the fetal heart rate of 15 bpm or more above baseline lasting 15 seconds or more. Before 32 weeks of gestation, the threshold is 10 bpm for 10 seconds. Accelerations indicate an intact fetal autonomic nervous system. A reactive nonstress test requires two or more accelerations within 20 minutes. The presence of accelerations is highly reassuring.

### Decelerations

#### Early Decelerations

Early decelerations have a gradual onset, with at least 30 seconds from onset to nadir. They mirror contractions, meaning their onset, nadir, and recovery coincide with the contraction. They are caused by fetal head compression triggering a vagal response. Early decelerations are benign and require no intervention.

#### Late Decelerations

Late decelerations also have a gradual onset with at least 30 seconds from onset to nadir. They begin after the contraction onset, reach their nadir after the contraction peak, and recover after the contraction ends. They are caused by uteroplacental insufficiency and are concerning. When accompanied by moderate variability, the fetus is likely compensating and not yet acidotic. When accompanied by absent or minimal variability, there is high concern for fetal acidemia.

#### Variable Decelerations

Variable decelerations have an abrupt onset, reaching their nadir in less than 30 seconds. They involve a drop of 15 bpm or more lasting at least 15 seconds but less than 2 minutes. They are variable in shape, timing, and relationship to contractions, caused by umbilical cord compression, and are the most common type of deceleration. Atypical features that suggest worsening fetal status include slow return to baseline, overshoots (tachycardia following the deceleration), absent variability within the deceleration, and a biphasic shape.

#### Prolonged Deceleration

A prolonged deceleration is a decrease of 15 bpm or more lasting 2 minutes or longer but less than 10 minutes. A deceleration lasting more than 10 minutes is classified as bradycardia. Causes include cord prolapse, uterine rupture, maternal hypotension, tachysystole, rapid cervical dilation, and epidural bolus.

<image>Strip examples of the four types of fetal heart rate decelerations (early, late, variable, and prolonged) with simultaneous contraction tracings below, showing the characteristic timing relationship between each deceleration type and uterine contractions</image>

## Three-Tier Fetal Heart Rate Classification

### Category I (Normal)

Category I tracings have a baseline of 110 to 160 bpm, moderate variability, no late or variable decelerations, and early decelerations and accelerations that may or may not be present. These tracings require routine monitoring with no intervention needed.

### Category II (Indeterminate)

Category II encompasses any tracing that does not meet Category I or Category III criteria. This is a very broad classification that includes tachycardia or bradycardia with moderate variability, minimal or absent variability without recurrent decelerations, marked variability, recurrent variable decelerations with moderate variability, recurrent late decelerations with moderate variability, and prolonged decelerations. Management involves continued monitoring, evaluation, intrauterine resuscitation, and determining whether the tracing trajectory is improving or worsening.

### Category III (Abnormal)

Category III tracings are defined by either absent variability with recurrent late decelerations, absent variability with recurrent variable decelerations, absent variability with bradycardia, or a sinusoidal pattern. The sinusoidal pattern is a smooth, undulating, sine wave-like tracing associated with severe fetal anemia. Category III tracings require immediate evaluation, intrauterine resuscitation, and preparation for expedited delivery if no improvement occurs.

| Category | Criteria | Management |
|---|---|---|
| I (Normal) | Baseline 110-160, moderate variability, no late/variable decels; ± early decels/accels | Routine monitoring |
| II (Indeterminate) | Does not meet Category I or III (broad category) | Continued monitoring, intrauterine resuscitation, assess trajectory |
| III (Abnormal) | Absent variability + recurrent lates, recurrent variables, or bradycardia; OR sinusoidal pattern | Immediate evaluation, resuscitation, expedite delivery if no improvement |

## Systematic Interpretation Approach (DR C BRAVADO)

The DR C BRAVADO mnemonic provides a structured approach to tracing interpretation: DR stands for Determine Risk (maternal and fetal risk factors), C for Contractions (frequency, duration, intensity, and resting tone), BRA for Baseline Rate (110 to 160 is normal), V for Variability (moderate is reassuring), A for Accelerations (present or absent), D for Decelerations (type, timing, duration, and recovery), and O for Overall assessment (Category I, II, or III, with attention to trajectory).

## Intrauterine Resuscitation

### First-Line Interventions

Initial interventions include maternal repositioning to the left or right lateral position or hands and knees, an IV fluid bolus of 500 to 1,000 mL lactated Ringer solution, discontinuation or reduction of oxytocin, brief supplemental oxygen (though evidence for benefit is limited), correction of maternal hypotension with IV fluids or ephedrine if epidural-related, vaginal examination to assess for cord prolapse, and amnioinfusion with room-temperature normal saline via IUPC for recurrent variable decelerations.

### If Tachysystole Present

When tachysystole is identified, oxytocin should be reduced or stopped. Terbutaline 0.25 mg subcutaneously can be administered for uterine relaxation. Vaginal prostaglandins should be removed if in place.

### Fetal Scalp Stimulation

Digital stimulation of the fetal scalp during vaginal examination can provide important information. An acceleration in response to stimulation is highly predictive of a fetal pH above 7.20, which is reassuring. An absent acceleration is not necessarily ominous but warrants continued close monitoring.

### Vibroacoustic Stimulation

Vibroacoustic stimulation uses an artificial larynx or similar device applied to the maternal abdomen. It elicits an acceleration if the fetus is not acidotic. This technique is more commonly used during antepartum nonstress testing than during intrapartum monitoring.

<image>Flowchart for management of Category II fetal heart rate tracings, showing initial assessment, intrauterine resuscitation steps (repositioning, fluid bolus, oxytocin reduction, amnioinfusion), reassessment of tracing trajectory, and decision pathways toward continued labor versus expedited delivery</image>

## Decision-Making for Delivery

### When to Expedite Delivery

Indications for expedited delivery include a Category III tracing unresponsive to resuscitation, prolonged bradycardia unresponsive to intervention, and a worsening Category II tracing trajectory with declining variability and increasing frequency or severity of decelerations. Clinical context matters considerably, including gestational age, stage of labor, maternal status, and time to delivery by vaginal versus cesarean route.

### Mode of Delivery

If the cervix is fully dilated and the station is low, operative vaginal delivery may be faster than cesarean. If delivery is remote, expedited cesarean is indicated. Emergent cesarean is performed for cord prolapse, uterine rupture, or sustained bradycardia.

## Limitations of EFM

Continuous EFM has high sensitivity for fetal distress but low specificity, resulting in a high false-positive rate. The positive predictive value of a non-reassuring tracing for cerebral palsy is approximately 0.14%, meaning that 99.8% of abnormal tracings do not result in cerebral palsy. Continuous EFM increases cesarean and operative delivery rates without improving neonatal mortality or cerebral palsy rates compared to intermittent auscultation. There is significant inter-observer and intra-observer variability in tracing interpretation. Despite these limitations, continuous EFM remains the standard in most US labor units.

## Clinical Pearls

Moderate variability is the single most reassuring feature of the fetal heart rate tracing. It essentially excludes current fetal metabolic acidemia.

Category II is a broad catch-all category that includes the vast majority of intrapartum tracings. The focus should be on trajectory, whether the tracing is improving or worsening, rather than on a single snapshot.

A reactive acceleration in response to scalp stimulation is equivalent to a fetal pH above 7.20. This test should be considered before committing to operative delivery for a concerning tracing.

Amnioinfusion is effective for recurrent variable decelerations caused by cord compression but not for late decelerations caused by uteroplacental insufficiency.

A sinusoidal pattern is a Category III emergency. Severe fetal anemia from abruption, fetomaternal hemorrhage, or alloimmunization must be ruled out.

The false-positive rate of EFM is extremely high. Clinicians should resist the urge to perform cesarean based on a single deceleration in the setting of otherwise reassuring features.

Clinical context should always guide decision-making. A concerning tracing in a fully dilated multiparous patient may be best managed with a brief operative vaginal delivery rather than a 30-minute cesarean.

## References

- ACOG Practice Bulletin No. 106: Intrapartum Fetal Heart Rate Monitoring: Nomenclature, Interpretation, and General Management Principles (2009, reaffirmed 2022)
- Macones GA et al. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring. Obstet Gynecol. 2008;112:661-666
- Clark SL et al. The limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia. Am J Obstet Gynecol. 2017;216:163.e1-6
- Alfirevic Z et al. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst Rev. 2017
- Simpson KR et al. Fetal heart rate assessment and intrauterine resuscitation. MCN Am J Matern Child Nurs. 2020