The position of your cervix could change during menstruation, usually moving lower down the vagina. Get through at least one period to see how your cervix height fluctuates to establish if you need to trim the stem. See if you need the stem for removal on any of the days you are on your period. If your cup sits comfortably in your vagina and the stem does not stick out, then you do not need to trim it. However, if the cup is inserted correctly and you have worn it for some time, and the stem pokes your underwear or sticks out of your vagina, consider trimming your stem. (Some cups' stem should not be trimmed - refer to individual product pages for more info.)
Be absolutely sure before you modify your cup. Don't lop off the entire stem at once; you can always trim more later but you can never put any back.
Never attempt to trim the cup’s stem while it is still inside of you; remove the cup before you trim the stem.