Background: Mean sac diameter (MSD) is a sonographic measurement of the gestational sac which is usually first seen at around 5 weeks, when it measures about 2-3 mm, It's the average of measurements taken in three dimensions.Crown rump length (CRL) defined as the length of the embryo or fetus from the top of it's head to bottom of torso, it's the most accurate estimation of gestational age in early pregnancy, it's determined by the average of three measurements of the longest fetal length. Aim of the study Determine efficacy of mean sac diameter minus crown rump length (MSD-CRL) in prediction of early pregnancy outcome. Methods: The study included 80 cases at (6:9) gestational weeks with singletone pregnancy. We examined the case at the initial visit, Mean sac diameter and Crown rump length were calculated for each case. The difference between the MSD and CRL in mm was calculated. Then follow up visit after two weeks later. Pregnancy outcome was then recorded between (11:14w). During transvaginal ultrasound (TVUS) we observed location, size, number and regularity of gestational sac. Cardiac pulsation & Presence or absence of sub-chorionic hematoma. Results: 73 cases (91, 3%) continued normal pregnancy and 7 cases (8, 8%) had pregnancy failure. It was found that the age, body mass index, gravidity and history of abortion show insignificant relation with outcome (p >0.05). Area under a curve was 0.984, p Value was <0.001, 95% CI was (0.961 – 1.000), at the cut off value (MSD-CRL) less than or equal 4, the sensitivity was 71.4%, the specificity was 97.2%, PPV was 71.4% and NPV was 97.3%, while at cut off value less than or equal 5, the sensitivity was 100.0%, specificity was 95.89, PPV was 70.0% and NPV was 100.0%. Conclusions: (MSD- CRL) is good prediction for early pregnancy outcome but, the optimum threshold for predicting pregnancy outcome needed to be established by further studies, also bigger sample size will provide more advantage.