Objective: To investigate the predictive power of maternal serum levels of progesterone, β-HCG and CA-125 each separately and in combination for predicting the prognosis in cases of threatened abortion. Study design: prospective study was conducted on 250 pregnant women who were entered into the study when their pregnancies were between the 5th and 7th gestational weeks and were followed up till their 20th week of gestation, venous blood samples were collected from all pregnant women between 5th and 7th gestational week for serum progesterone, β-HCG and CA125 Patients included in the study were divided according to outcome into Group I: Patients with threatened abortion and ongoing pregnancy till 20th weeks of gestation, Group II: Patients with threatened abortion and their pregnancies ended by spontaneous abortion, Group III: Patients with normal pregnancy (did not suffer from threatened or spontaneous abortion). Results: 39 Patients with threatened abortion and ongoing pregnancy till 20th weeks of gestation, 23 Patients with threatened abortion and their pregnancies ended by spontaneous abortion, 188 Patients with normal pregnancy (did not suffer from threatened or spontaneous abortion). Serum progesterone combined with β HCG determinations Showed the greatest diagnostic accuracy (97.77 %), sensitivity (95.5 %) and specificity (98%) and largest AUC (ROC) 0.998 (95%CI 0.938to1.000). Conclusion: serum progesterone and β-HCG are good predictors of spontaneous abortion in cases of threatened abortion while CA-125 is poor predictor for that if any.