The special design of Medela?s Nipple Shield, which is worn over the nipple and areola, permits the flow of breastmilk and provides a larger surface for baby to latch on to. However, because they may diminish the stimulation needed to sustain lactation, nipple shields should be used only under professional care. Weekly weight checks are recommended during use. Available in standard size only (16mm). One shield per pack. Personal care item - cannot be returned.