Proper fit of a breast shield for pumping breast milk

This figure shows the appropriate fit of a breast shield for pumping breast milk. The nipple should be centered and should move easily within the tunnel of the shield without rubbing against the sides. If a breast shield is too small, the nipple will rub against the sides of the tunnel, causing discomfort and possible trauma, resulting in milk ejection inhibition and poor milk flow. If a breast shield is too large, a loss or reduction in suction will occur due to air leakage, resulting in ineffective stimulation, milk ejection, and milk flow.