Fetal heart rate
A normal fetal heart rate (FHR) usually ranges around 120-160 beats per minute (bpm) in the in utero period.
Evolution through gestation
Although the myocardium begins to contract rhythmically by 3 weeks following-conception (from spontaneously depolarising myocardial pacemaker cells in the embryonic heart) it is first visible on sonography ~ 6 weeks of gestation where is usually around 100-120 beats per minute (bpm).
This then increases progressively over the subsequent 2-3 weeks becoming 7
- ~ 110 bpm (mean) by 5-6 weeks
- ~ 170 bpm by 9-10 weeks
This is followed by a decrease becoming on average.
- ~ 150 bpm by 14 weeks
- ~ 140 bpm by 20 weeks
- ~ 130 bpm by term
Although the healthy fetus the heart rate is usually regular, a beat-to-beat variation of approximately 5 - 15 beat per minute can be allowed.
A slow fetal heart rate is termed a fetal bradycardia : this is usually defined as 1
- a heart rate below 100 bpm before 6.3 weeks' gestation or
- a heart rate below 120 bpm at 6.3 - 7.0 weeks
A rapid fetal heart rate is termed a fetal tachycardia : this is usually defined as
- a heart rate above 160-180 bpm 5,7.
- a rate of ~ 170 bpm may be classified as a borderline fetal tachycardia
- 1. Doubilet PM, Benson CB, Chow JS. Outcome of pregnancies with rapid embryonic heart rates in the early first trimester. AJR Am J Roentgenol. 2000;175 (1): 67-9. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Doubilet PM, Benson CB. Embryonic heart rate in the early first trimester: what rate is normal? J Ultrasound Med. 1995;14 (6): 431-4. J Ultrasound Med (abstract) - Pubmed citation
- 3. Benson CB, Doubilet PM. Slow embryonic heart rate in early first trimester: indicator of poor pregnancy outcome. Radiology. 1994;192 (2): 343-4. Radiology (abstract) - Pubmed citation
- 4. Doubilet PM, Benson CB. Outcome of first-trimester pregnancies with slow embryonic heart rate at 6-7 weeks gestation and normal heart rate by 8 weeks at US. Radiology. 2005;236 (2): 643-6. doi:10.1148/radiol.2362040880 - Pubmed citation
- 5. Oudijk MA, Visser GH, Meijboom EJ. Fetal tachyarrhythmia--part I: Diagnosis. Indian Pacing Electrophysiol J. 2004;4 (3): 104-13. Indian Pacing Electrophysiol J (link) - Free text at pubmed - Pubmed citation
- 6. Laboda LA, Estroff JA, Benacerraf BR. First trimester bradycardia. A sign of impending fetal loss. J Ultrasound Med. 1989;8 (10): 561-3. J Ultrasound Med (abstract) - Pubmed citation
- 7. Hornberger LK, Sahn DJ. Rhythm abnormalities of the fetus. Heart. 2007;93 (10): 1294-300. doi:10.1136/hrt.2005.069369 - Free text at pubmed - Pubmed citation
Synonyms & Alternative Spellings
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|Foetal heart rate||✗|
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|Embryonic heart rate (EHR)||✗|