Fetal Heart Rate Tachycardia Definition
Fetal tachycardia is defined as a baseline fetal heart rate greater than 160 beats per minute (bpm) sustained for 10 minutes or longer. 1
Standard Definition Across Guidelines
- The American Academy of Family Physicians and NICHD consensus define fetal tachycardia as a baseline FHR exceeding 160 bpm 1
- This threshold is consistently applied across international guidelines, with the notable exception of FIGO which uses >150 bpm as their cutoff 2
- The baseline must be sustained for at least 10 minutes to be classified as tachycardia rather than a transient acceleration 1
Normal Baseline Range Context
- Normal baseline FHR is defined as 110-160 bpm 1, 3
- The fetal heart rate physiologically decreases slightly as gestation advances, with the 90th percentile at 40 weeks being approximately 150 bpm 4, 5
- Fetuses with baseline rates between 150-160 bpm at term (≥40 weeks) represent a "high-normal" range that warrants closer surveillance, as this has been independently associated with increased risk of meconium-stained fluid, cesarean delivery for fetal distress, and neonatal acidemia 5
Clinical Significance in Augmentation
- During labor augmentation with oxytocin, fetal tachycardia (>160 bpm) should prompt immediate evaluation for maternal fever, infection, hyperthyroidism, or fetal hypoxia 3
- If tachycardia develops during augmentation, discontinue oxytocin immediately and implement general resuscitative measures including left lateral positioning, oxygen administration (6-10 L/min), IV fluid bolus, and maternal vital sign assessment 3
- The presence of moderate variability (6-25 bpm) with tachycardia is reassuring and predicts absence of fetal acidemia, whereas absent variability combined with tachycardia is concerning and may indicate fetal compromise 1, 3