Background: According to estimates, between 30% and 40% of implanted pregnancies end in spontaneous abortion in the first trimester, with the majority happening fairly early on. Objectives: To evaluate gestational sac (GS) diameter and shape, yolk sac (YS) diameter and shape, embryonic heart rate (EHR) and crown rump length (CRL) during the first trimester as prognostic factors of first trimester pregnancy outcome. Patients and Methods: This prospective observational cohort study was carried out on 118 patients in Shebin Elkom Teaching Hospital and Menoufia University Hospital in uncomplicated singleton pregnancy from (20-35) years old women. Results: 109 cases (92.4%) resulted in an ongoing pregnancy and entered the 2^nd trimester successfully, while 9 cases (7.6%) resulted in miscarriage. There was a highly statistically significant decrease in GS diameter, CRL, fetal heart rate but increase in YS diameter in fetal loss group more than ongoing pregnancy at 6, 9 and 12 weeks. Conclusion: The best indicator of the prognosis for first trimester pregnancy outcomes was YS diameter measurement. Fetal heart rate, GS diameter, and CRL diameter were the next best predictors, and an increase in YS diameter beyond what is expected for any gestational age (GA) and a decrease in any of these factors are indicators of poor pregnancy outcomes during the first 12 weeks of pregnancy.