Introduction
Fetal monitoring is an essential part of intrapartum care. Whether using an external cardiotocograph (CTG) or an internal fetal scalp electrode, interpreting the fetal heart rate (FHR) tracing is critical for evaluating fetal well-being, guiding interventions, and ensuring safe delivery.
This article provides a step-by-step, evidence-based guide on how to read a fetal monitor, including baseline heart rate, variability, accelerations, decelerations, and contraction patterns. It follows international standards from ACOG, FIGO, and NICE.
What Is a Fetal Monitor?
A fetal monitor is a medical device used during pregnancy and labor to measure and record the fetal heart rate (FHR) and uterine contractions. It helps obstetricians, midwives, and nurses assess fetal wellbeing and detect signs of distress early, ensuring safer deliveries.
Fetal monitoring is an essential part of modern obstetrics. It provides real-time data that guides clinical decisions such as induction, augmentation, use of medications, or emergency delivery.
Two main types exist:
1.External fetal monitoring
• Doppler ultrasound transducer for fetal heart rate
• Tocotransducer for contractions
2.Internal fetal monitoring
• Fetal scalp electrode (FSE) for heart rate
• Intrauterine pressure catheter (IUPC) for contractions
External monitoring is non-invasive and most commonly used.
Understanding a Fetal Monitor Tracing
A fetal monitor displays two main graphs:
1. Upper Graph – Fetal Heart Rate (FHR)
Measured in beats per minute (bpm).
2. Lower Graph – Uterine Contractions
Measured using a toco reading or mmHg (if internal).
Reading fetal monitoring involves analyzing five key components:
• Baseline Fetal Heart Rate
• Variability
• Accelerations
• Decelerations
• Uterine Contraction Pattern
Let's break them down.
1. Baseline Fetal Heart Rate (Normal: 110–160 bpm)
The baseline is the baby’s average heart rate over a 10-minute window.
What is Normal?
• 110–160 bpm = Normal
• >160 bpm = Tachycardia
• <110 bpm = Bradycardia
Causes of Abnormal Baseline
Tachycardia: Infection, maternal fever, fetal hypoxia, medications
Bradycardia: Cord compression, fetal hypoxia, maternal hypotension
2. Variability (The Most Important Indicator of Fetal Oxygenation)
Variability reflects how the heart rate fluctuates from beat to beat.
Types of Variability
• Absent: No variation → concerning
• Minimal: <5 bpm → may be due to sleep, medication, hypoxia
• Moderate: 6–25 bpm → normal and reassuring
• Marked: >25 bpm → may indicate stress or stimulation
Why Variability Matters
Moderate variability is the strongest sign that the baby is well-oxygenated.
3. Accelerations (Good Sign)
Accelerations are temporary increases in fetal heart rate.
Definition
• Increase of ≥15 bpm
• Lasting ≥15 seconds
Meaning
Accelerations indicate:
• Good fetal oxygenation
• Healthy central nervous system
• No signs of distress
Accelerations = Reassuring.
4. Decelerations (May Be Normal or Concerning)
Decelerations are drops in fetal heart rate and are classified by shape and relationship to contractions.
Types of Decelerations
4.1. Early Decelerations
• Mirror contractions
• Caused by head compression
• Benign and normal during labor
4.2. Variable Decelerations
• Abrupt drops
• Due to umbilical cord compression
• Common, often correctable with position changes
4.3. Late Decelerations
• Begin after contraction starts
• End after contraction ends
• Due to uteroplacental insufficiency
• Concerning if persistent
When Decelerations Are Concerning
• Recurrent late decelerations
• Variable decelerations with loss of variability
• Prolonged deceleration (>2 minutes)
These require evaluation and possible intervention.
5. Interpreting Uterine Contractions
A contraction tracing shows:
• Frequency: minutes between contractions
• Duration: seconds each contraction lasts
• Strength: measured externally or with IUPC
• Resting Tone: should return to baseline between contractions
Normal Pattern
• 3–5 contractions in 10 minutes
• Adequate rest between contractions
Too many contractions (tachysystole = >5 in 10 minutes) can reduce fetal oxygenation.
Putting It All Together: The NICHD 3-Tier System
The U.S. NICHD (National Institute of Child Health and Human Development) classification system divides fetal monitor tracings into three categories:
Category I (Normal)
• Baseline 110–160
• Moderate variability
• No late or variable decelerations
• May include accelerations or early decelerations
→ Reassuring
Category II (Indeterminate)
Does not fit category I or III.
Examples:
• Minimal variability
• Variable decelerations
• Tachycardia
→ Requires monitoring and possible intervention
Category III (Abnormal)
• Absent variability with recurrent late decelerations
• Recurrent variable decelerations
• Bradycardia
• Sinusoidal pattern
→ Indicates fetal distress; intervention needed urgently
Common Clinical Interventions
For concerning tracings, providers may:
• Change maternal position
• Provide oxygen
• Give IV fluids
• Stop oxytocin
• Treat maternal hypotension
• Amnioinfusion for variable decelerations
• Prepare for operative delivery (if needed)
Conclusion
Reading a fetal monitor is an essential skill for managing labor and ensuring fetal safety. By understanding baseline heart rate, variability, accelerations, decelerations, and contraction patterns—and using NICHD classification—you can recognize reassuring patterns as well as warning signs.
Whether you are a healthcare student, nurse, midwife, or expectant parent, this structured approach provides a strong foundation for interpreting fetal monitor tracings with confidence.
References
1. National Institute of Child Health and Human Development (NICHD). Workshop Report on Fetal Heart Rate Monitoring.
2. American College of Obstetricians and Gynecologists (ACOG). Practice Bulletin on Intrapartum Fetal Heart Rate Monitoring.
3. Simpson KR, Creehan PA. Perinatal Nursing, 6th Edition.
4. Freeman RK, Garite TJ, Nageotte MP. Fetal Heart Rate Monitoring, 4th Edition.
5. RCOG Guidelines. The Use of Electronic Fetal Monitoring.
6. WHO. Intrapartum Care for a Positive Childbirth Experience.
