Methodology: This is a prospective study which was carried out at Cairo University Maternity Hospital in period of the November, 2012 up to July 2013. The study included 60 pregnant women during first trimester of their pregnancy (from 6 to 11 weeks of gestation) diagnosed as threatened abortion. Each pregnant woman was submitted to two ultrasound scans during the first trimester where (Crown- rump length, Fetal heart rate, Yolk sac diameter and Yolk sac volume measurement) were assessed by using 2D and 3D transvaginal ultrasound also, Single serum progesterone and serum β-HCG measurement were assessed. Complete questionnaire was performed including: obstetric history, and symptoms of the current pregnancy. Objectives: The primary outcome was to evaluate: the correlation between the ultrasound parameters assessed in the first trimester (Crown- rump length, Fetal heart rate, Yolk sac diameter and Yolk sac volume measurement) in first scan and the correlation between the ultrasound parameters in group A who continue normal and group B who turn missed miscarriages also, comparisons between different serum results of HCG and progesterone with gestational age in the first trimester threatened abortion to detect the relationship between serum progesterone and HCG levels and viability of pregnancy during the first trimester. Results: in the first scan, there were stronge positive correlation between gestational age by ultrasound and (CRL, YSD, YSV) while weak correlation with FHR. According to the second ultrasound scan we classified the result into two groups: group A included 29 pregnant women with threatened abortion who continue normal pregnancy while group B included 16 pregnant women with threatened abortion who turn missed miscarriages the means difference ultrasound parameters of GA by US; CRL, GSD, YSD and YSV between two groups were statistically significant. The better single predictor of threatened cases turn to missed miscarriages according to the ROC curves was yolk sac diameter using 2D transvaginal ultrasound but no significant differences were found when this parameter was compared with the predictive value of yolk sac volume using 3D transvaginal ultrasound. YSV using 3D US combined YSD using 2D US determinations showed the greatest diagnostic accuracy (91.1%) sensitivity (97 %) and specificity (81.3 %) so, combination of two ultrasound variables shows substantial improvement over uses one ultrasound parameter.Also, the better single predictor of non viable pregnancy according to the ROC was serum progesterone levels but no significant differences were found when this parameter was compared with the predictive value of β -HCG concentration. Serum progesterone combined with β-HCG determinations showed the greatest diagnostic accuracy (84.2 %) sensitivity (96.6%) and specificity (71.4%). combination of two biochemical parameters shows substantial improvement over a single-marker strategy.