OBJECTIVE To compile, for the first time, serial ultrasonographic findings during the first trimester of pregnancy in women with a history of primary recurrent spontaneous abortion so as to define the dynamics of early normal and abnormal gestations in this category of gravidas. METHODS Transvaginal ultrasonograms were obtained weekly from 5 to 12 weeks' gestational age in 40 women, 10 each of four groups: recurrent spontaneous aborters and primiparas (controls), with both successful and failed gestations. RESULTS Embryonic heart motion was detected in 40-50% of successful pregnancies during the fifth week of gestation and in the balance by the sixth week, while heart motion was detected in no more than 50% of pregnancies that later failed. Of the failed pregnancies, all were evident by the eighth week of gestation, including those with previously documented viability. The gestational sac size and crown-rump length were smaller than expected in both failed groups, with the sac size difference evident as early as week 5 and the crown-rump length difference apparent by week 7. CONCLUSIONS Appropriate timing of the initial ultrasonogram in recurrent aborters (i.e., 8 weeks' gestational age) can identify, by means of heart motion and gestational sac features, all pregnancies that will ultimately fail.