Using the correct size Breast Shield with your pump can help you to pump more effectively--you can get more milk, more comfortably. Medium is the default Medela size, which comes with all their pumps, and is the right size for most moms.  If you are pumping with size medium shields and feel that the shield is not adequately compressing your milk ducts, or if you have a lot of milk collecting in the shields instead of flowing into the bottle you may want to consider the small shields.  You will also need Personal Fit Connectors to use any of the Personal Fit Shields.   If you need more help choosing a shield read this article.

Works with all Medela pumps (with personal fit connectors).  BPA Free.

For hygienic reasons, breast pump parts, storage, and bottles cannot be returned once opened.