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 f ormulas for mean sac diameter and crown-rump length to data from the recent ly published US mifepristone-misoprostol abortion trial would-result in dif ferences in assigned gestational ages and a higher rate of complete abortio n. STUDY DESIGN: Data from the US mifepristone-misoprostol trial were reanalyz ed. The ultrasonographic findings at baseline examination of the 2121 parti cipants were used to estimate gestational age according to criteria establi shed by Rossavik et al for mean sac diameter and by Robinson and Fleming, H adlock et al, and Goldstein and Wolf son for embryonic pole. The gestationa l ages as assigned by the different criteria were then compared and the tre atment outcomes at various gestational ages were calculated for each of the dating criteria. These findings were compared with those reported in the o riginal study. RESULTS: Fourteen percent of study subjects were assigned to the incorrect gestational age group according to the criteria used for the original repor t. Still, outcomes according to gestational age group were similar regardle ss of which ultrasonographic gestational age criteria were used and were co mparable to those calculated in the original report. Overall efficacy for s ubjects at less than or equal to 42 days' gestation was 95% to 96%, compare d with 91% for subjects at between 43 and 49 days' gestation, when the vari ous criteria were used. CONCLUSIONS: The results from the United States mifepristone-misoprostol ab ortion study were not altered by applying modern and appropriate ultrasonog raphic dating formulas. The rate of complete abortion was highest among sub jects at less than or equal to 42 days' gestation.