The timing of a repeat ultrasound examination in the evaluation for ectopic pregnancy.

A method is described for timing a repeat ultrasound examination in patients evaluated for ectopic pregnancy in whom the findings are initially non-diagnostic. This method is based on measuring the serum hCG at the time of the initial ultrasound examination, which allows the time interval required for the serum hCG to exceed 6500 mIU/ml to be calculated. When the serum hCG is above this level, the gestational sac of an intrauterine pregnancy can be reliably identified, and failure to do so signifies ectopic gestation. Seven patients referred for ultrasound to rule out ectopic pregnancy had initially nondiagnostic findings. In each case, a correctly-timed repeat examination, demonstrating a gestational sac, enabled the diagnosis to be excluded.