What Nina asks is possible by paying a little attention. If you are using the ring according to the instructions (as for all combined hormonal methods), your menstrual flow (withdrawal bleeding) will begin during the ring-free interval. If you want to change the start day of the flow, you can shorten the ring-free interval (but never lengthen it!)
For example, if your menstrual flow usually starts on Thursday and you want to change it to Monday (3 days earlier), you will have to start the following month. All you have to do is insert the new ring 3 days earlier than usual.
If your ring-free interval is very short (e.g. it lasts 3 days or even less), you may not have the usual withdrawal bleeding, but could manifest spotting (small spots or drops of blood) during the use of the next ring.
If you’re not sure how to proceed, or if you have any questions, don’t hesitate to contact your gynecologist for clarification.
