Background: Approximately 15-20% of the pregnancies are terminated by miscarriage. Yolk sac first appears at about 5 weeks gestation and is visualized by ultrasound and embryonic heart rate can be used as prognostic factors for first trimester pregnancy outcome. The aim of this study was to evaluate the yolk sac size and embryonic heart rate and to examine whether these parameters could serve as a prognostic factors for the first trimester pregnancy outcome. Methods: The study included 52 pregnant women in their first trimester from 6 weeks till 12 weeks gestation. Informed consent was taken from every patient.This study conducted at outpatient clinic of radiology department at maternity unit of Zagazig University Hospitals during the period from November 2016 till May 2017. Results: These cases allocated into 4 groups; according to gestational age The vast majority of YSD in the studied groups had normal sac diameter (80.8%).There was a positive significant correlation between YSD and gestational age in miscarriage group (Group IV), while non significant correlation in other groups. EHR of miscarriage group IV was highly significant lower than that of other groups. EHR of miscarriage group IV was highly significant lower than that of other groups. Conclusion: Abnormal yolk sac diameter, in the form of small, enlarged, absent or irregular yolk sac, and embryonic bradycardia are associated with poor pregnancy outcome; independent of maternal risk factors such as age, body mass index or parity.