Endovaginal US: demonstration of cardiac activity in embryos of less than 5.0 mm in crown-rump length.

The authors reviewed the endovaginal ultrasonographic (US) findings for 96 patients with embryos with crown-rump lengths of less than 5.0 mm. Of the 71 patients with adequate follow-up, initial endovaginal US demonstrated cardiac activity in 46 embryos and no cardiac activity in 25. Initial endovaginal US failed to demonstrate cardiac activity in five of 40 normal embryos, three with crown-rump lengths of less than 2.0 mm and two, between 2.0 and 3.9 mm. Endovaginal US identified cardiac activity in all 12 normal embryos with crown-rump lengths of 4.0-4.9 mm. The presence of cardiac activity was associated with a 24% risk of spontaneous abortion. In embryos between 2.0 and 4.9 mm in crown-rump length, absent cardiac activity was associated with a 91% risk of abortion. All 17 patients with vaginal bleeding and embryos demonstrating no cardiac activity subsequently aborted. The embryonic yolk sac was absent in 35% of patients who subsequently aborted. Variation outside of the 95% confidence limits of the mean for crown-rump length compared with mean gestational sac diameter and yolk sac diameter was also helpful in predicting an abnormal outcome. Nonvisualization of cardiac activity at endovaginal US in embryos less than 4.0 mm in crown-rump length may be normal and warrants follow-up US examination.