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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.

Related pathology

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

A rapid and irregular fetal heart rate is usually termed a fetal tachyarrhythmia.

See also

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