Objectives : To determine the clinical value of a Mean Gestational Sac Diameter,Yolk Sac Characteristics and Retrochorionic blood flow during the First Trimesterand Pregnancy Outcome.Patients and Methods _; a prospective study was conducted including 100 pregnantpatients between 7 and 11 weeks of gestation complaining of mild vaginal bleedingtransvaginal sonography was done to measure the mean sac diameter Yolk SacCharacteristics and Retrochorionic blood flow during the First Trimester andPregnancy Outcome. Patients were followed up by vaginal sonography at weeklyintervals till the end of the first trimester.Results : This present study included 100 pregnant women. The patients classifiedinto three groups. First Group (40 patients): Patients with bad obstetric history, e.g.,previous abortion, preterm labour, IUGR. Second Group (40 patients): Patientscomplaining of mild vaginal bleeding and the cervical internal os was closed(threatened abortion) with positive fetal life. Third Group (Control Group) (20patients): Patients who has good obstetric history, multipara with no history ofpregnancy wastage.Conclusion : abnormal yolk sac characteristics were significantly associated with badobstetric outcome the presence of dilated and/or echogenic yolk sac was significantlyassociated with bad obstetricoutcom