When Can a Fetal Heartbeat Be Detected on Ultrasound?

Timeline of Cardiac Detection

• Transvaginal ultrasound: Cardiac activity visible as early as 5.5–6 weeks gestation (3–4 weeks post-conception).
• Transabdominal ultrasound: Usually 6.5–7 weeks (later with higher BMI).
• Doppler handheld: Audible heartbeat ~10–12 weeks.

Clinical Significance

• Confirms intrauterine pregnancy (vs. ectopic).
• Indicates embryonic viability (heart rate 100–180 bpm).
• Gestational age dating: CRL measurement ±3–5 days accuracy at 7–10 weeks.

If No Heartbeat Is Seen

• May be too early (dates off, irregular cycles).
• Repeat scan in 7–10 days.
• Correlate with serial β-hCG (should double ~48 hrs in early pregnancy).
• If CRL ≥7 mm with no cardiac activity → nonviable (missed abortion).

Early pregnancy uncertainty is common. Follow-up clarifies.