Objective: The aim of this study was to compare long-term use of combined oral contraceptive (COC) after gonadotropin-releasing hormone (GnRH) agonist plus add-back therapy with dienogest (DNG) treatment as medical treatments after surgery for ovarian endometrioma.

Methods: This prospective cohort study analyzed 52 reproductive-aged women who underwent surgery for ovarian endometrioma and received postoperative medical treatment with either COC after GnRH agonist (n = 20) or DNG (n = 32) for 24 months. Changes in quality-of-life (QOL) and bone mineral density (BMD) were compared according to treatment. In addition, recurrence of pain and lesions were compared.

Results: Baseline characteristics did not differ in demographic profiles and factors associated with endometriosis or QOL. During 24 months of treatment, no differences in any component of QOL were found between the two groups. BMD at the lumbar spine significantly decreased after the first 6 months of treatment in both COC after GnRH agonist (-3.5%) and DNG (-2.3%) groups, but the groups did not differ statistically. After 6 months, further decrease in BMD was not observed until 24 months in both groups. In addition, no cases of pain or endometrioma recurrence were found.

Conclusion: Our results suggest that long-term use of COC after GnRH agonist plus add-back therapy is comparable to dienogest as a long-term postoperative medical treatment for endometriosis.