The flange (sometimes called a breast shield) is the cup placed over the breast during pumping to create a vacuum seal. This seal draws the nipple into the tunnel for milk extraction, mimicking the action of a baby feeding. Using the correct flange size is fundamental for comfortable and efficient pumping. An improper fit can cause discomfort, damage breast tissue, and reduce milk output. Finding the right fit helps maintain a healthy milk supply and prevents issues like clogged ducts.
Visual and Physical Signs of an Oversized Flange
When a flange is too large, the tunnel diameter allows too much breast tissue to be pulled in past the nipple. A key visual sign is the areola—the darker skin surrounding the nipple—being significantly drawn into the tunnel. Observing more than about one-quarter inch of the areola entering the funnel indicates this excessive tissue movement.
An oversized flange often results in a painful tugging sensation felt specifically at the base of the nipple or across the areola. The nipple may move too freely within the tunnel, bouncing back and forth or side to side. This loose fit can also cause the sides of the nipple to rub and chafe against the tunnel wall.
A flange that is too big can compromise the pump’s ability to stimulate the milk ducts and fully drain the breast. You might notice a reduced volume of milk compared to previous sessions, or a feeling that the breast is not completely softened and empty after pumping. This incomplete milk removal can negatively affect milk production over time.
Symptoms that Indicate a Flange is Too Small
If a flange is too small, the nipple will rub intensely against the sides of the tunnel throughout the pumping cycle. This friction can lead to sharp, localized pain felt primarily at the tip or shaft of the nipple.
Visually, an undersized flange causes the nipple to look compressed or flattened during pumping. After a session, the nipple may appear blanched (white or discolored due to restricted blood flow), or a white ring may be visible at the base of the nipple. This constriction prevents the nipple from expanding properly during the milk ejection reflex, resulting in poor suction and a low milk yield.
Calculating Your Correct Flange Size
The most reliable method to determine the proper flange size is to measure the diameter of the nipple base. This measurement should be taken when the nipple is relaxed, ideally before a pumping or feeding session, as size can temporarily increase after milk expression. Use a flexible ruler or measuring tape to find the width of the nipple across the base, measuring in millimeters. Measure the nipple tissue only, excluding the areola.
Once the nipple diameter is measured, the rule of thumb is to select a flange size that is 2 to 4 millimeters larger. For example, an 18-millimeter nipple diameter suggests a flange size between 20 and 22 millimeters. This allowance provides the necessary space for the nipple to move freely and for the tissue to swell slightly during the pumping process.
Nipple size can change over the course of your pumping journey, and even between the left and right breast. Re-measurement may be necessary if you experience renewed pain or a drop in supply. If the calculated size still feels uncomfortable, small adjustments within the 2 to 4 millimeter range can be made to find the optimal fit for comfort and milk output.