What is a normal fetal heart rate (FHR) in pregnancy?

Normal Fetal Heart Rate in Pregnancy

The normal fetal heart rate (FHR) during pregnancy is 110-160 beats per minute (bpm), as defined by international guidelines and the American Academy of Family Physicians. 1, 2, 3

Baseline FHR Parameters

• The accepted normal range is 110-160 bpm, which represents the standard used for clinical decision-making during pregnancy and labor 1, 2, 3
• Baseline FHR 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 3
• Tachycardia is defined as sustained baseline >160 bpm for at least 10 minutes, while bradycardia is defined as <110 bpm for at least 10 minutes 1, 3

Gestational Age Variations

• FHR decreases progressively throughout pregnancy, with higher rates in early gestation and lower rates near term 4, 5
• First trimester mean FHR is approximately 151 bpm (range 135-167 bpm) 5
• Second trimester mean FHR is approximately 145 bpm (range 139-151 bpm) 5
• Third trimester mean FHR is approximately 125 bpm (range 119-131 bpm) 5
• At 40 weeks gestation, the 90th percentile of FHR is consistently around 150 bpm, meaning rates between 150-160 bpm, while technically "normal," may warrant closer monitoring 6

Clinical Context and Reassuring Features

• Moderate variability (6-25 bpm) is the most reassuring finding and predicts absence of fetal acidemia, regardless of where the baseline falls within the normal range 2, 3
• The presence of accelerations (≥15 bpm above baseline lasting ≥15 seconds) indicates fetal well-being 1
• A reactive non-stress test requires two or more accelerations meeting these criteria during 20 minutes of observation 3

Important Caveats

• Fetal sleep cycles lasting 20-40 minutes can cause temporary decreased variability without indicating fetal compromise—this is a common pitfall in interpretation 1, 3
• Maternal medications including analgesics, anesthetics, barbiturates, and magnesium sulfate can decrease FHR variability without representing true fetal distress 1, 3
• Maternal fever, infection, hyperthyroidism, or certain medications can cause fetal tachycardia and should be evaluated when heart rate exceeds 160 bpm 2, 3
• At term (≥40 weeks), FHR between 150-160 bpm is associated with higher risk of meconium-stained fluid, cesarean delivery for fetal distress, and neonatal acidemia, despite being within the "normal" range 6

Abnormal Ranges Requiring Evaluation

• FHR >160 bpm sustained for ≥10 minutes requires assessment for maternal fever, infection, medications, hyperthyroidism, or fetal causes 1, 2, 7
• FHR <110 bpm sustained for ≥10 minutes requires evaluation for sinus node dysfunction, complete heart block, or other bradyarrhythmias 7
• Irregular rhythms most commonly result from premature atrial contractions, which are usually benign, but persistent irregularity warrants further evaluation 7