[Fetal heart rate during labour: definitions and interpretation]

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Neonatal Monitoring

Context:

• Continuous fetal heart rate monitoring is standard practice in labor, even for low-risk pregnancies.
• Accurate interpretation of fetal heart rate (FHR) patterns is crucial for fetal well-being.
• Existing guidelines for FHR interpretation require consensus and clear definitions.

Purpose:

• To define normal and abnormal fetal heart rate (FHR) patterns during labor.
• To clarify the interpretation of various FHR decelerations (early, variable, late, prolonged).
• To identify FHR patterns predictive of fetal acidosis and guide clinical decision-making.

Summary:

• Normal FHR tracing: baseline 110-160 bpm, moderate variability (6-25 bpm), accelerations, no decelerations. Abnormalities include tachycardia (>160 bpm) and bradycardia (<110 bpm).
• Decelerations are classified by onset and timing relative to contractions: early, variable, late, and prolonged. Variability can be minimal or absent.
• Patterns predictive of fetal acidosis include recurrent late/variable/prolonged decelerations, bradycardia with absent variability, and sudden severe bradycardia. Non-reassuring patterns require consideration of risk factors and additional methods like scalp sampling.

Impact:

• Standardized interpretation of FHR patterns can reduce diagnostic errors and the high false positive rate of electronic fetal monitoring.
• Improved interpretation may lead to a decrease in unnecessary operative deliveries.
• Clearer guidelines enhance the ability to detect fetal distress and improve neonatal outcomes.