So . . . my Medela pump came with size Medium shields. As did my accessory kit. After holding one up to my nipple, I think I definitely need size small ones. Should I wait until after I have the baby and talk with a lactation specialist before buying a smaller size? Does the nipple size change after birth?

And, if I do need a smaller size, what the heck should I do with the 4 size Medium ones I already have?!? I can't return them to the store - do you think I could sell them on Craigslist and just list them as "never been used - too big for me, needed a smaller size"?