Fetal Heart Rate Pattern Interpretation
Core concepts
Interpretation uses four features: baseline rate, variability, accelerations, and decelerations. Normal baseline is 110 to 160 beats per minute. Variability is the fluctuation in baseline and reflects autonomic nervous system integrity; moderate variability (6 to 25 beats per minute) is generally reassuring. Minimal variability can reflect sleep, medications, or hypoxia; absent variability is concerning, especially with decelerations.
Decelerations are classified by timing relative to contractions. Early decelerations mirror contractions and reflect head compression; they are benign. Variable decelerations are abrupt and often reflect cord compression. Late decelerations begin after the contraction peak and reflect uteroplacental insufficiency. Prolonged deceleration lasts at least two minutes. Sinusoidal pattern is a smooth undulating baseline without variability and is concerning.
Traps
The classic trap is calling a late deceleration early because the timing is close. Look at the onset relative to the contraction, not the depth. Another trap is treating variability alone as reassuring while ignoring recurrent late decelerations. Also remember that accelerations are reassuring but their absence is not automatically non-reassuring in all gestational ages.
Rule of thumb
Recurrent late or variable decelerations with minimal or absent variability require intervention; moderate variability with no decelerations is generally reassuring.
Worked example
A tracing shows a baseline of 140, moderate variability, and decelerations that begin after each contraction peak and recover slowly. These are late decelerations. The response is intrauterine resuscitation: reposition, oxygen per protocol, intravenous fluids, and reduce uterine activity if excessive, while preparing for further evaluation.