Fajr Adil: Understanding Fetal Heartbeat on First Trimester Ultrasound
Fajr Adil, Sonographer at Al-Shakireen Hospital, shared a post on LinkedIn:
“First Trimester Ultrasound Series | Day 4
Fetal Cardiac Activity (Fetal Heartbeat)
Detection of fetal cardiac activity is one of the most reassuring findings in early pregnancy and an important indicator of embryonic viability.
Ultrasound Features
- Usually detected by transvaginal ultrasound at 5.5–6 weeks of gestation.
- Best assessed using M-mode ultrasound rather than spectral Doppler during the first trimester to minimize fetal ultrasound exposure.
- Normal fetal heart rate increases rapidly in early pregnancy.
Normal Fetal Heart Rate
- ~6 weeks: 90–110 bpm
- 7–8 weeks: 120–170 bpm
- 8–10 weeks: 150–180 bpm
- After 10 weeks: usually 110–160 bpm
Clinical Pearl
If the CRL is ≥7 mm with no detectable cardiac activity on a high-quality transvaginal ultrasound, this is diagnostic of early pregnancy failure.
Learning Point
Always document:
- Presence of fetal heartbeat.
- Fetal heart rate (FHR).
- Crown-Rump Length (CRL).
- Gestational age.
Question for discussion:
Which ultrasound mode is recommended for measuring fetal heart rate during the first trimester: M-mode or Spectral Doppler?”

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