The criteria for diagnosing nonviability in early pregnancy should aim for a specificity of 100%, meaning false positive results should be virtually eliminated. Current data suggest that using specific cutoff values for crown-rump length, mean sac diameter, and certain time-based criteria can help diagnose nonviability with high accuracy. A Crown–rump length (CRL) of ≥7 mm and no heartbeat and mean sac diameter of ≥25 mm and no embryo are diagnostic for early pregnancy failure.