Objectives: The frequency of adnexal masses in pregnant women ranges from 0.1% to 4%. Selecting the right approach to manage the subsequent intervention remains one of the most controversial challenges among gynecologists. Our aim in this cross-sectional study was to clarify the clinical-pathological differences among the adnexal masses that are excised during either the antepartum period or cesarean section (CS). Methods: In this study, we assessed 11,000 pregnancy cases referred to the Qaem Hospital in the Mashhad University of Medical Sciences, Iran, between 2010 and 2014. In total, 53 pregnant women with adnexal masses (other than non-gynecological mass and ectopic pregnancy) were selected for further investigation. We divided patients into two groups (group A and group B). Patients of group A had a diagnosed tumor that was excised antepartum while patients in group B had a mass taken out during CS. We then assembled data based on maternal age, parity, gestational age, surgery type, delivery mode, size and location of the tumor, complications, presentations, histopathological diagnosis, and ultrasonography findings for further analysis. Results: The major proportion of masses (62.3%) were excised during CS whereas the remainder (37.7%) were removed antepartum. The mean size of the detected tumor for benign and malignant cases was 10.0 cm and 13.8 cm in group A, and 8.0 cm and 9.3 cm in group B, respectively. There was a statistically significant difference observed between patients in the two groups regarding the benign/malignant status of the mass (p = 0.008), its size (p = 0.019) and simplicity/complexity (p = 0.004). Conclusions: The rate of malignant tumors was considerably higher in women who had antepartum mass excision compared to those with mass resection during CS. Also, tumors were larger (and more complex) in patients in group A compared to group B.