What are the normal fetal heart rate ranges per gestational age?

From the Guidelines

Fetal heart rate ranges vary throughout pregnancy, with a normal range at term being 110-160 beats per minute (bpm) 1. The fetal heart rate is an important indicator of fetal well-being, and its monitoring is crucial during pregnancy and labor.

Key Points to Consider

• In early pregnancy, the fetal heart rate typically starts around 100-115 bpm, increasing to 140-170 bpm by 7-9 weeks 1.
• During the late first trimester and into the second trimester, the rate peaks at approximately 155-195 bpm, before gradually decreasing and stabilizing in the second and third trimesters 1.
• The normal range at term (37-42 weeks) is 110-160 bpm, with transient variations outside this range possible during contractions 1.
• Heart rate patterns, including baseline rate, variability, accelerations, and decelerations, provide valuable information about fetal well-being throughout pregnancy 1.

Monitoring and Interpretation

• The National Institute of Child Health and Human Development (NICHD) categorization is used to interpret fetal heart rate tracings, with Category I indicating a normal tracing, Category II indicating an indeterminate tracing, and Category III indicating an abnormal tracing 1.
• The DR C BRAVADO mnemonic is a useful tool for interpreting continuous electronic fetal monitoring, taking into account factors such as risk, contractions, baseline rate, variability, accelerations, and decelerations 1.
• Persistent abnormalities in fetal heart rate patterns may indicate fetal distress, hypoxia, or other complications requiring medical intervention 1.

Clinical Implications

• Monitoring fetal heart rate ranges and patterns is essential for identifying potential complications and ensuring the best possible outcomes for mother and baby 1.
• Clinicians should be aware of the normal ranges and patterns of fetal heart rate at different stages of pregnancy and labor, and be able to interpret and respond to abnormal tracings appropriately 1.

From the Research

Fetal Heart Rate Ranges per Gestation

• The normal fetal heart rate ranges between 110 and 160 beats per minute 2, 3, 4
• Fetal heart rate decreases slightly during gestation 3
• Embryonic heart rates below 90 beats per minute at 6 to 8 weeks of gestation have been shown to be associated with a high likelihood of subsequent first trimester demise 5
• The lower limit of normal is 100 beats per minute up to 6.2 weeks' gestation and 120 bpm at 6.3-7.0 weeks 5

Abnormal Fetal Heart Rates

• A fetal heart rate is considered abnormal if the heart rate is beyond the normal ranges or the rhythm is irregular 2
• Tachyarrhythmias (heart rate in excess of 160 beats/min) and bradyarrhythmias (heart rate <110 beats/min) are considered abnormal 2
• Abnormal baseline heart rate during 10 minutes or more is termed tachycardia above 160 bpm and bradycardia below 110 bpm 4

Fetal Heart Rate Monitoring

• Continuous fetal heart rate monitoring is widely used during labor even in low risk pregnancies 4
• Electronic fetal monitoring is a method to detect risk of fetal asphyxia; analysis and interpretation of FHR patterns are difficult with a high false positive rate, increasing operative deliveries 4