The Medela PersonalFit Breastshield medium is for average sixed nipples--because one size does not fit all. Medela's wide range of PersonalFit breastshields allows mothers to choose the breastshield that is the right size for them, to ensure maximum comfort and efficiency when pumping. Designed for individual maximum comfort, personalised breastshield size for most comfortable pumping, maximum output and optimised breast emptying. Made from 100% Bisphenol-A free materials for the health of your baby.The right breastshield size and a proper fit avoid compression of any milk ducts during pumping. As a consequence the mother is given the best chance of protecting her milk volume, optimising breast emptying, preventing nipple trauma and pumping with comfort. This will help a mother to maintain her milk production and support her lactation. Using a too small or too large breastshield may lead to impaired milk removal because milk ducts could get blocked or milk ejection-inhibited. Over time, this can result in reduced daily milk output, which will decrease milk production and can lead to early weaning. Friction around the nipple and/or areola can cause discomfort and trauma which may cause a mother to only pump infrequently. Again, her milk production is jeopardised. Tissue breakdown due to nipple trauma carries the risk of infection and mastitis.