Ovulation was defined as having 2 or more consecutive progesterone concentrations \>16 nmol/L within 5 days, confirmed by ultrasound evidence of ovulation (follicular rupture or preceding presence of a follicle-like structure \>15 mm in size).

Maximum progesterone (Max P) was defined as the maximum progesterone value. Ovulation was defined as 2 or more consecutive progesterone concentrations \>16 nmol/L within 5 days during the 3 treatment cycles, supported by ultrasound evidence of ovulation. The Max P values greater than 16 nmol/L are presented by vaginal ring group and cycle.

Breakthrough bleeding and/or spotting (BTB-S) is defined as any bleeding or spotting episode that occurred during the expected non-bleeding period that was neither an early nor a continued withdrawal bleeding. Bleeding = any bloody vaginal discharge that required one or more sanitary pads or tampons per day; Spotting = any bloody vaginal discharge that required no sanitary pads or tampons per day.