Normal Fetal Heart Rate at 8 Months of Gestation
The normal fetal heart rate at 8 months (approximately 32-36 weeks) of gestation is 110-160 beats per minute, with the most current guidelines establishing this as the standard range for clinical practice. 1
Baseline Heart Rate Parameters
At 32 weeks and beyond, the normal baseline fetal heart rate ranges from 110-160 bpm, which represents the standard accepted by the American Academy of Family Physicians and international guidelines 1, 2
The fetal heart rate physiologically decreases slightly as pregnancy advances, so at 8 months gestation, heart rates toward the lower end of the normal range (110-120 bpm) are more common than in earlier pregnancy 2
Baseline heart rate is defined as the mean heart rate rounded to increments of 5 bpm during a 10-minute segment, excluding accelerations, decelerations, and periods of marked variability 1
Assessment During Monitoring
When performing non-stress testing at this gestational age, a reactive test requires two or more fetal heart rate accelerations of 15 beats/minute above baseline lasting 15 seconds during 20 minutes of observation 1, 3
Moderate variability (6-25 bpm) is the most reassuring finding and indicates normal fetal oxygenation and acid-base balance, regardless of where the baseline falls within the normal range 1, 4
Tachycardia is defined as a baseline heart rate above 160 bpm (though some guidelines use >150 bpm), while bradycardia is defined as below 110 bpm, both sustained for at least 10 minutes 1, 5
Clinical Context and Pitfalls
Fetal sleep cycles lasting 20-40 minutes can cause temporary decreased variability without indicating fetal compromise, which is a common pitfall in interpretation 1, 3
Maternal medications including analgesics, anesthetics, barbiturates, and magnesium sulfate can decrease fetal heart rate variability without representing true fetal distress 1, 4
Research suggests that at 40 weeks gestation, the 90th percentile of fetal heart rate is around 150 bpm, meaning that sustained rates of 150-160 bpm at term may warrant closer observation, though this is still within the normal range 2, 6
Maternal fever, infection, hyperthyroidism, or medications can cause fetal tachycardia and should be evaluated when heart rate exceeds 160 bpm 4