A breast pump flange (or breast shield) is the funnel-shaped piece of equipment that fits over the nipple and areola to create the vacuum seal necessary for milk expression. As the primary interface between the pump and the body, its size is the most important factor for both comfort and efficiency. An accurate flange size ensures milk is removed effectively and completely, supporting a consistent milk supply. Finding the correct fit is necessary to prevent discomfort and maximize the amount of milk expressed during each session.
The Physiology of Proper Sizing
The precise fit of the flange matters because it mechanically dictates how the breast tissue is stimulated and drained. When the pump is active, the nipple is gently drawn into the flange tunnel, mimicking the action of an infant’s mouth during nursing. This movement needs to be free and rhythmic to stimulate the milk ejection reflex and allow milk to flow efficiently.
If the flange is sized incorrectly, the delicate milk ducts beneath the areola can become compressed or blocked, leading to inefficient milk removal. A size that is too small can cause the nipple to rub against the tunnel walls, resulting in painful friction or trauma, such as blistering or blanching. Conversely, a flange that is too large may pull in excessive areola tissue, which can also compress ducts and reduce the overall milk output. The right fit prevents injury and maximizes the volume of milk collected by ensuring the breast is adequately emptied.
Step-by-Step Nipple Measurement
Determining the correct flange size begins with accurately measuring the nipple diameter. This measurement should be taken before a pumping session when the nipple is relaxed and unstimulated. Use a ruler or a flexible measuring tape marked in millimeters (mm) for precision.
Measure the diameter across the base of the nipple, where the nipple tissue meets the areola. Measure only the nipple itself, not the surrounding areola tissue. Measuring the nipple at the tip, rather than the base, is a common mistake that often leads to selecting a flange size that is too small.
Once the base diameter is measured, the final flange size is calculated by adding a small buffer. The guideline is to add 2 to 4 millimeters to the measured nipple diameter. This additional space accounts for the slight expansion and movement of the nipple tissue that occurs once suction is applied during pumping. For example, if your nipple measures 17 mm, your ideal flange size would be between 19 mm and 21 mm.
Identifying Correct and Incorrect Fit During Pumping
The measurement provides a starting point, but the true test of fit happens when the pump is running. A correctly sized flange allows only the nipple to move freely back and forth within the tunnel without rubbing against the sides. You should observe minimal or no areola tissue being pulled into the tunnel, and the experience should be comfortable with no sharp pain or pinching.
Several indicators signal that a flange size is incorrect and needs adjustment. If the flange is too small, the nipple will rub painfully against the tunnel walls, and the tip may appear white or blanched after the session due to restricted blood flow. If the flange is too large, a significant amount of the areola will be pulled deeply into the tunnel along with the nipple.
If the fit is poor, you may notice a tugging sensation, discomfort, or a feeling that the breast is not fully draining. Ineffective milk removal, often evidenced by low output, is a strong signal to re-evaluate the flange size. Observing the nipple’s movement and your comfort level during the first two minutes of pumping is a reliable way to validate the initial measurement.
Handling Sizing Challenges and Variations
Sizing complexities often arise that simple measurement alone cannot resolve. One frequent variation is asymmetry, where individuals require different flange sizes for each breast to ensure optimal comfort and milk expression. It is important to measure and assess both nipples independently, as using a mismatched size can lead to pain or reduced output.
Another challenge involves tissue elasticity (elastic nipples), where the nipple stretches significantly down the length of the tunnel under suction. If the nipple hits the back of the tunnel, even a seemingly correct size may cause discomfort and ineffective drainage. Using a flange with a longer tunnel or a soft silicone insert that gently holds the tissue back may be a better solution than changing the rigid flange diameter.
Size can also change over the course of the pumping journey, particularly postpartum. Swelling and engorgement common in the early days can temporarily alter the nipple size. If pumping becomes uncomfortable or output decreases weeks or months after finding a good fit, a re-measurement may be necessary to adapt to the body’s changing state.