Approximately 30-40% of implanted pregnancies result in spontaneous abortion during the first trimester. Intrauterine gestational sac appears sonographically, followed by the yolk sac and the fetal pole with cardiac activity. Yolk sac and early embryonic heart rate (EHR) are detected easily by transvaginal sonography. Our purpose was to examine whether yolk sac diameter (YSD) and early EHR could serve as prognostic factors in evaluating pregnancy outcome in 200 pregnant women, examined using 2D transvaginal ultrasonography in the first trimester. Fetal heart rate was measured by M-mode and YSD was determined by placing the calipers on the inner limits of the longer diameter. 184(92%) resulted in an ongoing pregnancy and entered the 2nd trimester successfully, while 16 (8%) resulted in miscarriages. Of the 16 fetal losses, 6 were missed abortions, 4 blighted ovums, 4 incomplete abortions and 2 complete abortions. The maximal embryonic heart rates presented at 9 weeks of gestation were 159 bpm, and then the fetal heart rates gradually decreased to 136 bpm at 12 weeks of gestation. According to yolk sac out of 194 cases with round and regular yolk sac shape, 184 had normal outcome and 10 had failed pregnancy. 6 cases had irregular shaped yolk sac and were diagnosed as abortion on follow up. Therefore, the important ultrasonographic findings suggestive of a poor outcome for the first trimester were the finding of: a small for date CRL, small gestational sac diameter, irregular shape of yolk sac and fetal bradycardia.