Fetal heart rate in the first and second trimester
Citation, DOI & article data
- Embryonal heart rate
- Embryonic heart rate
- Embryonic heart rate (EHR)
A normal fetal heart rate (FHR) usually ranges from 120 to 160 beats per minute (bpm) in the in utero period. It is measurable sonographically from around 6 weeks and the normal range varies during gestation, increasing to around 170 bpm at 10 weeks and decreasing from then to around 130 bpm at term.
Evolution through gestation
Although the myocardium begins to contract rhythmically by 3 weeks after conception (from spontaneously depolarizing myocardial pacemaker cells in the embryonic heart) it is first visible on sonography around 6 weeks of gestation. The FHR is then usually around 100 to 120 beats per minute (bpm).
FHR 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 in FHR becoming on average:
- ~150 bpm by 14 weeks
- ~140 bpm by 20 weeks
- ~130 bpm by term
Although in the healthy fetus the heart rate is usually regular, a beat-to-beat variation of approximately 5 to 15 beats per minute can be allowed.
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Related pathology
A slow fetal heart rate is termed fetal bradycardia and is usually defined as 1:
- FHR <100 bpm before 6.3 weeks gestation, or
- FHR <120 bpm between 6.3 and 7.0 weeks
A rapid fetal heart rate is termed a fetal tachycardia and is usually defined as:
- FHR >160-180 bpm 5,7
- FHR around 170 bpm may be classified as borderline fetal tachycardia
A rapid and irregular fetal heart rate is usually termed a fetal tachyarrhythmia.
See also
References
- 1. Doubilet P, Benson C, Chow J. Outcome of Pregnancies with Rapid Embryonic Heart Rates in the Early First Trimester. AJR Am J Roentgenol. 2000;175(1):67-9. doi:10.2214/ajr.175.1.1750067
- 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 P & Benson C. 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
- 5. Oudijk M, Visser G, Meijboom E. Fetal Tachyarrhythmia--Part I: Diagnosis. Indian Pacing Electrophysiol J. 2004;4(3):104-13. PMC1501076
- 6. Laboda L, Estroff J, Benacerraf B. First Trimester Bradycardia. A Sign of Impending Fetal Loss. J Ultrasound Med. 1989;8(10):561-3. doi:10.7863/jum.1989.8.10.561
- 7. Hornberger L & Sahn D. Rhythm Abnormalities of the Fetus. Heart. 2007;93(10):1294-300. doi:10.1136/hrt.2005.069369
- 8. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/fetal-heart-monitoring#:~:text=The%20average%20fetal%20heart%20rate,to%20conditions%20in%20your%20uterus.
- 9. Benson C & Doubilet P. Slow Embryonic Heart Rate in Early First Trimester: Indicator of Poor Pregnancy Outcome. Radiology. 1994;192(2):343-4. doi:10.1148/radiology.192.2.8029394
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