The breast pump flange, also known as the breast shield, is the funnel-shaped component that forms a seal around the breast and draws the nipple into its central tunnel to express milk. Using the correct size is the single most important step for both comfort and maximizing the amount of milk collected during a pumping session. A correctly sized flange ensures the pump can effectively mimic the natural sucking motion of a baby, which is necessary for efficient milk removal.
Why Flange Size Is Critical for Pumping Success
The dimensions of the breast shield directly influence the physiological response of the breast to the pump’s vacuum. An ill-fitting flange can compress the milk ducts located just beneath the areola, which impedes milk flow and results in incomplete breast drainage. This incomplete emptying signals to the body that less milk is needed, potentially leading to a gradual decrease in milk supply over time.
Incorrect sizing also increases the risk of pain and physical damage, which can inhibit the let-down reflex. Excessive friction or pressure can lead to trauma such as blistering, bruising, or chafing. The resulting pain interferes with the release of oxytocin, which triggers the milk ejection reflex. Poor milk removal also increases the likelihood of developing painful conditions like clogged ducts or mastitis.
Step-by-Step Guide to Measuring Your Nipple
To find the right size, first measure the diameter of your nipple when it is in a relaxed state. Use a ruler or a specialized measuring tool to find the diameter across the base of the nipple, where it meets the areola. Measure only the nipple itself, excluding any surrounding areola tissue.
Measure both nipples individually, as it is common for them to be different sizes, which may require using two different flange sizes. After determining the diameter in millimeters, add an allowance of 2 to 4 millimeters to calculate your estimated flange size. This added space accounts for the natural swelling and expansion of the nipple tissue during pumping.
Nipple size can change throughout the lactation period, sometimes increasing after the milk supply is fully established or fluctuating throughout the day. Re-measure your nipples periodically or whenever you experience a change in comfort or milk output. This ensures your equipment continues to accommodate the dynamic nature of your breast tissue.
Recognizing Signs of a Poor Fit
Observing your nipple during a pumping session is as important as the initial physical measurement. If the flange is too small, the nipple will rub painfully against the sides of the tunnel, causing friction and potentially restricting the amount of tissue drawn in. You may notice only the very tip of the nipple moving back and forth, indicating that not enough tissue is being stimulated for effective milk expression.
Conversely, a flange that is too large allows an excessive amount of the areola to be pulled deep into the tunnel with the nipple. This causes pain around the base of the nipple and areola due to swelling and compression of the underlying tissue. A telltale sign of an incorrect fit is the “lipstick shape” of the nipple immediately after pumping, where the tip appears blanched, flattened, or angled. This misshapen appearance indicates friction or compression that requires an immediate size adjustment.
When to Seek Professional Assistance
If you have tried multiple flange sizes based on accurate measurements and still experience persistent pain, low milk output, or nipple damage, consult a specialist. A Certified Lactation Consultant (IBCLC) can visually assess the fit and pumping technique in real-time, often identifying subtle issues difficult to self-diagnose. They can help address specific anatomical variations that standard sizing guides may not cover.
One such variation is “elastic nipples,” where the tissue stretches excessively far down the flange tunnel under vacuum, sometimes hitting the back of the shield. This overstretching can cause pain and inefficient milk removal even with the theoretically correct flange size. In these cases, an IBCLC can recommend specialized solutions, such as using silicone flange inserts or cushions, which provide a gentler, more customized fit and help manage the unique elasticity of the tissue.