Adjuvant therapies are often used to enhance endometrial thickness during IVF. This retrospective cohort analysis investigated if women undergoing oocyte donation cycles with sonographic evidence of endometrial insufficiency benefit from adjuvant medicaltherapy. Infertile patients received 503 mock cycles followed by 503 anonymous oocyte donation cycles. One hundred and twenty-three patients received adjuvant therapy during a donor oocyte cycle. Patients who had a mock endometrial thickness ≥8 mm experienced a significant decrease in endometrial thickness with the donor oocyte cycle regardless of the use of adjuvant therapy (P < 0.001). In contrast, those patients with a mock endometrial thickness