Background: Threatened Obstetricians are quite concerned about miscarriage occurring during the first trimester. It is still a clinical problem to identify pregnant women at risk of miscarriage early on. One promising serum biomarker for the prediction of unfavourable pregnancy outcomes is CA-125. The purpose of this research was to determine if serum CA125 has a predictive role in threats of abortion during the first trimester and in the 20-week follow-up. Methods: A cross-sectional research was conducted with 90 participants, 45 of whom were pregnant normally (Group A) and 45 of whom were pregnant with a risk of miscarriage (Group B). Following a defined procedure, thorough clinical evaluations were carried out, which included obtaining medical history, doing physical exams, conducting laboratory investigations, performing transvaginal ultrasounds, and evaluating CA-125 levels. Up to the 20th week of pregnancy, patients were monitored. It was shown that the group experiencing a miscarriage had significantly higher serum CA-125 levels (77.55 ± 26.38 IU/ml vs. 42.97 ± 14.09 IU/ml, p < 0.0001). With a sensitivity of 91.7% and specificity of 86.4%, a CA-125 cut-off value of 31.87 was associated with a statistically significant increased risk of miscarriage. Results: There is a strong correlation between elevated blood CA-125 levels and certain clinical indicators and the risk of miscarriage during the first trimester.