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Fetal heart rate

A normal fetal heart rate (FHR) usually ranges from 120 to 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 around 6 weeks of gestation where is usually around 100 to 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 to 15 beat per minute can be allowed.

Related pathology

A slow fetal heart rate is termed a fetal bradycardia and is usually defined as 1

  • a heart rate below 100 bpm before 6.3 weeks gestation, or 
  • a heart rate below 120 bpm between 6.3 and 7.0 weeks 

A rapid fetal heart rate is termed a fetal tachycardia and is usually defined as 

  • a heart rate above 160-180 bpm 5,7
  • a rate around 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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