The value of serial human chorionic gonadotropin testing as a diagnostic tool in ectopic pregnancy

This study examines the sensitivity of serial human chorionic gonadotropin determinations in the detection of ectopic pregnancy for patients who present with human chorionic gonadotropin titers less than 6500 mIU/ml. A log human chorionic gonadotropin time curve was used to calculate the slope of change. A slope below 0.11 (85% confidence limit for intrauterine gestations) is used as the cutoff value. Of 50 patients with serial titers at sampling intervals of 2 to 5 days, 26 (49%) had falling values and 22 had subnormal slopes. Only five had initially normal slopes and two of these patients eventually had falling titers. The sensitivity of an abnormal slope (below 0.11) in the detection of ectopic pregnancy was 90%. A 12.5% false positive rate was found in a group of 24 intrauterine pregnancies.