I've been using cups for a year and a half. Never had anything close to a leak. This period started and I decided to use my medium MeLuna. I noticed right away it didn't seem to be working well. I felt wet and alot of slobber. So I went back to the bathroom after ten minutes, and there was a lot of slobber. More than ever, so I concluded I thought it was leaking on me. I couldn't figure out why. I switched to the large, and no problem. (Keep in mind, the only difference between the two cups is the legnth.) Well today I figured out what was going on: It's my uterus. It has always sat very low on my period. Well, for whatever reason, this month it didn't drop down--I can barely touch the end of it with my tip of my finger. Normally, I only have to put my finger in up to my middle knuckle to feel it, and I always put my cups in as far back as I can get it to go. Meaning, with my finger in all the way, I can feel my uterus against the entire top-legnth of my finger. Not this month! My MeLuna is a ball stem, medium, so it's very short for my normaly low uterus. The MeLuna sets down where the ball is just inside my vagina. I believe this was too low for my unusualy high uterus to set in, so it wasn't catching all the blood. I now KNOW for a FACT your cervix has to be in the cup to work without leaking. The medium MeLuna was just too short this month.