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At what point should embryonic cardiac activity be detected on Ultrasound?
Embryonic cardiac activity is usually visible as soon as an embryo is detectable sonographically, often at a CRL as small as 2 mm.
The absence of sonographically detectable embryonic cardiac activity by a CRL ≥7 mm is diagnostic of a failed pregnancy, as is the absence of an embryo with a heartbeat ≥2 weeks after an US examination demonstrates a gestational sac without a yolk sac, and absence of an embryo with a heartbeat ≥11 days after an US demonstrating a gestational sac with a yolk sac.
Between 5 and 8 weeks, the embryonic heart rate is usually 100 beats/min or greater. From 8 weeks to term, the average heart rate is 140 beats/min (range 120 to 180 beats/min). The thresholds for bradycardia based on embryonic size are listed in the below table.
Thresholds for Bradycardia Based on Embryonic Size
CROWN RUMP LENGTH (MM) | BRADYCARDIA (BEATS PER MINUTE) |
---|---|
<5 | <80 bpm |
5-9 | <100 bpm |
10-15 | <110 bpm |