Normal Fetal Heart Rate Range
The normal fetal heart rate (fetal heart tone) ranges from 110-160 beats per minute throughout gestation, as defined by international guidelines and consensus statements. 1, 2, 3
Baseline Parameters
The accepted normal baseline fetal heart rate is 110-160 bpm, which represents the mean heart rate rounded to increments of 5 bpm during a 10-minute segment, excluding accelerations, decelerations, and periods of marked variability. 2
This range is consistently recommended by the American Academy of Family Physicians and represents the NICHD consensus definition used for clinical practice. 1, 3
Tachycardia is defined as a baseline heart rate above 160 bpm sustained for at least 10 minutes, while bradycardia is defined as below 110 bpm sustained for the same duration. 2, 3
Gestational Age Considerations
The fetal heart rate decreases slightly as pregnancy progresses toward term. 4
At 40 weeks gestation or beyond, the 90th percentile of fetal heart rate has been consistently found at around 150 bpm, though the upper limit of normal remains 160 bpm. 5
Fetuses at 40 weeks or beyond with baseline heart rates between 150-160 bpm (though still technically "normal") have been associated with higher rates of labor complications, including meconium-stained amniotic fluid, cesarean section for fetal distress, and neonatal acidemia. 5
Clinical Context and Reassuring Features
Moderate variability (6-25 bpm) is the most reassuring finding and predicts the absence of fetal acidemia, regardless of where the baseline falls within the normal 110-160 bpm range. 1, 2, 3
A reactive non-stress test requires two or more fetal heart rate accelerations of 15 beats/minute above baseline lasting 15 seconds during 20 minutes of observation. 2
Common Pitfalls to Avoid
Fetal sleep cycles lasting 20-40 minutes can cause temporary decreased variability without indicating fetal compromise, which is a common misinterpretation. 1, 2
Maternal medications including analgesics, anesthetics, barbiturates, and magnesium sulfate can decrease fetal heart rate variability without representing true fetal distress. 1, 2
Maternal fever, infection, hyperthyroidism, or certain medications can cause fetal tachycardia above 160 bpm and should be evaluated as potential causes rather than assuming primary fetal pathology. 1, 2, 3