Use of various ultrasonographic criteria to evaluate the efficacy of mifepristone and misoprostol for medical abortion

Objective: This study was undertaken to determine whether applying modern formulas for mean sac diameter and crown-rump length to data from the recently published US mifepristone-misoprostol abortion trial would result in differences in assigned gestational ages and a higher rate of complete abortion. Study Design: Data from the US mifepristone-misoprostol trial were reanalyzed. The ultrasonographic findings at baseline examination of the 2121 participants were used to estimate gestational age according to criteria established by Rossavik et al for mean sac diameter and by Robinson and Fleming, Hadlock et al, and Goldstein and Wolfson for embryonic pole. The gestational ages as assigned by the different criteria were then compared and the treatment outcomes at various gestational ages were calculated for each of the dating criteria. These findings were compared with those reported in the original study. Results: Fourteen percent of study subjects were assigned to the incorrect gestational age group according to the criteria used for the original report. Still, outcomes according to gestational age group were similar regardless of which ultrasonographic gestational age criteria were used and were comparable to those calculated in the original report. Overall efficacy for subjects at ≤42 days’ gestation was 95% to 96%, compared with 91% for subjects at between 43 and 49 days’ gestation, when the various criteria were used. Conclusions: The results from the United States mifepristone-misoprostol abortion study were not altered by applying modern and appropriate ultrasonographic dating formulas. The rate of complete abortion was highest among subjects at ≤42 days’ gestation. (Am J Obstet Gynecol 1999;181:1419-24.)