A menstrual cup may not be sealed properly if its slightly dented or not fully ballooned open on insertion. You can check to see if its fully opened by inserting a forefinger into the vaginal canal & reaching up towards the rim of the Cup & gently feeling around to see if its dented or still folded.
If there are signs of spotting after insertion, follow these simple steps to create a "leak proof suction" & to ensure the menstrual cup is properly ballooned & "sealed" after insertion.
For the cup not to leak, its important to ensure the cervix is INSIDE the cup. The cervix feels like the pointed tip of your nose or thumb & forefinger pressed together with that dent in between them.
1) The cup needs to be gently turned clockwise or counter-clockwise inside the vaginal canal or moved around gently by grabbing hold of the base or mid section of cup. It could also be slightly pulled out & re-inserted such that it can suck in air & fully balloon open.
2) Another helpful tip is to insert the thumb & forefinger in on either side of the cup & push back gently against the vaginal walls to create space/air that the cup can suck up & fully open. The push back should be high up near the rim & possible.
3) Try to swirl your finger around the cup to remove any excess blood left in the vagina from spotting & wipe or preferably rinse off blood left on the labia after the steps above to accurately ascertain if the cup is still not sealed & causing the leaks.