I have the Medela PIS with the standard 24 mm breast shields. Pumping is uncomfortable so I started reading up on whether I needed a different size breast shield. From what I read, everything indicated that I should be using a larger breast shield. That is until I read that if a woman has nipples the size of quarters then a large is the right size and half dollar size nipples warrant an extra large. My nipples are not even close to a quarter in size (if it is the circumference of the actual nipple, mine are smaller than a dime) which made me think a small might be the appropriate size for me. But like I said, all of my "symptoms" are in line what needing a larger shield. Does anyone know anything about this stuff?