Hello Cristiana
The size of the breast does not really matter, but the size of the nipple does. There are 2 different sizes, one 18mm and one 24mm.

LG

Hello Christina89, as Melissa has written, the size of the breast shield has nothing to do with the size of the breast, but with the size of the nipple. The delivery includes 2x2 sizes (21mm and 24mm) these two fit in most cases. The 27mm size will be available in March 2023. All the best, Medela Switzerland AG

Yes, for me it works (I use E or F depending on the brand). And if the two nipples sold with the pump are too small, you can apparently order a larger one. The 24 fits me fine.