Fetal Heart-Rate Assessment

Learning objectives

After completing this chapter, you should be able to obtain and verify a fetal heart-rate signal, distinguish maternal pulse artifact, determine baseline and variability, identify accelerations and decelerations, classify Category I, II, and III patterns, evaluate uterine activity, connect fetal changes to maternal physiology, and select appropriate stabilization, escalation, and diversion actions during transport.

Describe every tracing in the same order

1

Signal
Confirm fetal—not maternal—heart rate.

2

Baseline
Normal, bradycardic, or tachycardic.

3

Variability
Absent, minimal, moderate, or marked.

4

Periodic changes
Accelerations and decelerations.

5

Uterine activity
Frequency and fetal relationship.

6

Category and action
Reassure, evaluate, resuscitate, or expedite.

Opening transport scenario

A 30-week patient with preterm rupture of membranes is being transferred to a tertiary center. The initial fetal baseline is 145/min with moderate variability. After she is moved supine for loading, maternal blood pressure falls to 82/46 mm Hg. The tracing develops recurrent late decelerations and minimal variability. Left tilt and correction of maternal hypotension improve the pattern. The fetal tracing did not deteriorate in isolation—it reflected a maternal perfusion problem.

1. Obtaining and verifying the signal

External Doppler and electronic fetal monitoring can be affected by maternal movement, obesity, fetal position, multiple gestation, vibration, transducer displacement, and equipment artifact. Before interpreting a sudden change:

• Check the maternal pulse and compare it with the displayed rate.
• Reposition the fetal transducer and identify the point of strongest fetal signal.
• Inspect cables, battery, paper speed, alarm settings, and signal quality.
• Use intermittent Doppler or ultrasound confirmation when the continuous signal is uncertain and this is within capability.
• For multiple gestation, confirm that two distinct fetal rates are being monitored.

2. Baseline fetal heart rate

The baseline is the mean fetal heart rate rounded to increments of 5 beats/min during a 10-minute segment, excluding accelerations, decelerations, marked variability, and major baseline shifts. At least 2 minutes of identifiable baseline are required within that 10-minute segment.

3. Baseline variability

Reduced variability may occur with fetal sleep, prematurity, magnesium, opioids, sedatives, hypoxia, or acidemia. The duration, gestational age, medication exposure, baseline, and associated decelerations determine urgency.

4. Accelerations

At 32 weeks and later, an acceleration rises at least 15 bpm above baseline for at least 15 seconds and less than 2 minutes. Before 32 weeks, a 10-bpm rise lasting at least 10 seconds is commonly used. Prolonged accelerations last 2 to less than 10 minutes. A change lasting 10 minutes or longer is a new baseline.

5. Decelerations

Early decelerations

Gradual decreases that mirror contractions. They are often associated with fetal head compression and usually do not require intervention when the rest of the tracing is reassuring.

Late decelerations

Gradual decreases shifted after the contraction. Recurrent late decelerations can reflect impaired uteroplacental oxygen transfer from maternal hypotension, tachysystole, placental disease, hypoxemia, or other causes.

Variable decelerations

Abrupt decreases with variable timing, depth, and shape. They commonly reflect umbilical cord compression. Recurrent deep or prolonged variables, slow return to baseline, reduced variability, or bradycardia increase concern.

Prolonged deceleration

A decrease lasting at least 2 minutes but less than 10 minutes. Causes include maternal hypotension, cord prolapse, uterine rupture, placental abruption, tachysystole, rapid descent, or medication effect. Ten minutes or longer is a baseline change.

6. Sinusoidal pattern

7. Uterine activity and fetal response

Normal uterine activity is five or fewer contractions in 10 minutes averaged over 30 minutes. Tachysystole is more than five in 10 minutes averaged over 30 minutes. Describe whether decelerations are present. Excessive frequency, prolonged contractions, or inadequate resting tone can reduce uterine perfusion between contractions.

8. Three-tier classification

9. Maternal-fetal corrective actions

10. Monitoring limitations during transport

• Vehicle motion and vibration increase artifact.
• Transducers can shift during loading, turns, and patient repositioning.
• External tocodynamometry estimates frequency and duration but not true contraction strength.
• Maternal habitus, fetal position, gestational age, and multiple gestation can reduce signal quality.
• Intermittent Doppler may be necessary when continuous monitoring cannot be maintained.
• Document periods of signal loss and the method used to reassess.

11. Evolving case study

Phase 1: Baseline

The 30-week patient has a baseline of 145/min, moderate variability, and no decelerations. This is reassuring for the moment.

Phase 2: Maternal position change

After supine loading, maternal blood pressure falls and late decelerations appear. The team confirms the fetal signal, applies left tilt, and treats the maternal perfusion problem.

Phase 3: Incomplete recovery

Blood pressure improves but the tracing retains minimal variability with recurrent late decelerations. The team stops any uterotonic stimulation, reassesses oxygenation and bleeding, contacts the receiving obstetric team, and identifies the nearest surgical-capable destination.

Phase 4: Destination decision

The tertiary center is 35 minutes away and a capable obstetric center is 8 minutes away. Persistent fetal deterioration despite maternal correction supports diversion discussion rather than blind adherence to the original plan.

12. High-yield chapter summary

1. Verify that the displayed rate is fetal, not maternal.
2. Normal baseline is 110–160/min.
3. Baseline requires at least 2 minutes in a 10-minute segment.
4. Moderate variability is 6–25 bpm.
5. At 32 weeks and later, accelerations are generally 15 bpm for 15 seconds.
6. Early decelerations mirror contractions.
7. Late decelerations are delayed and suggest uteroplacental compromise.
8. Variable decelerations are abrupt and commonly reflect cord compression.
9. Prolonged decelerations last 2 to less than 10 minutes.
10. Tachysystole is more than five contractions in ten minutes averaged over thirty minutes.
11. Category I is reassuring; Category II is indeterminate; Category III is abnormal.
12. Correct the maternal mechanism first.
13. Use oxygen for maternal indication, not reflexively in a normally oxygenated patient.
14. Persistent abnormal patterns require escalation and possible diversion.

References

1. International Board of Specialty Certification. Maternal Fetal Transport Microcredential Candidate Handbook. Updated April 2026.
2. American College of Obstetricians and Gynecologists. Intrapartum Fetal Heart Rate Monitoring: Interpretation and Management. Clinical Practice Guideline No. 10. 2025.
3. Macones GA, et al. The 2008 NICHD workshop report on electronic fetal monitoring. Obstet Gynecol. 2008;112:661–666.
4. American College of Obstetricians and Gynecologists. Fetal Heart Rate Nomenclature, Interpretation, and Management. Educational module.
5. American College of Obstetricians and Gynecologists. First and Second Stage Labor Management. Clinical Practice Guideline No. 8. 2024.