en Original Article Original Article <strong>Background:</strong> CA-125 is a glycoprotein and its origin is uncertain during pregnancy. It arises during the first trimester and return to a non-pregnancy range in late pregnancy.<br> <strong>Objective:</strong> The aim of this study was to compare CA-125 level in threatened abortion and normal pregnancy less than 20 weeks of pregnancy.<br> <strong>Materials and Methods:</strong> This was a prospective case study carried out on 50 healthy pregnant (group 1) and 50 threatened abortion women (group 2). We compared the levels of CA-125 in these groups and followed them to be informed of the outcome of pregnancy.<br> <strong>Results:&nbsp;</strong>Fifty percent of women were in 20-24 years old group, primigravida and in the first trimester of pregnancy. The mean level of CA-125 in group 1 was 26.2 &plusmn; 3.25 IU/ml and in group 2 was 37.44 &plusmn; 2.72 IU/ml. The mean level of CA-125 in finally aborted patients was 58.17&plusmn;7.25 IU/ml and in normal pregnant women, who continue to term, was 26.61&plusmn;1.76 IU/ml. The CA-125 level in threatened women,whose pregnancy continued and did not abort, was 30.89 IU/ml. There was statistically significant difference between mean serum CA-125 levels of two groups (<em>p</em> < 0.05), while there was no statistically significant difference between these levels in the patients of both groups who continued pregnancies (<em>p </em>> 0.1). In group 2, there was a statistically significant difference in the level of CA-125 between those who developed abortion and those whose pregnancy continued but not aborted (<em>p</em> < 0.05).<br> <strong>Conclusion: </strong>Measurement of serum CA-125 may be an inexpensive, easily available, sensitive and specific predictor of outcome in threatened abortion, which results the loss of pregnancy. CA-125, Pregnancy, Abortion, Threatened abortion 57 0 http://ijrm.ir/browse.php?a_code=A-10-549-278&slc_lang=en&sid=1 Sedigheh Ayaty ff_vahid @ yahoo.com Yes Ghaem Hospital-Mashhad University of Medical Sciences, Mashhad, Iran Fatemeh Vahid Roudsari No Ghaem Hospital-Mashhad University of Medical Sciences, Mashhad, Iran Fatemeh Tavassoly No Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, Iran