The breast pump flange, also known as a breast shield, is the cone-shaped piece that fits over the nipple and areola to create a seal for milk expression. Its purpose is to comfortably draw the nipple into the tunnel to stimulate the milk ejection reflex (let-down) and remove breast milk. Finding the right fit is important for both comfort and maximizing milk collection. Flange size can change throughout the pumping journey, making regular reassessment necessary.
Understanding Why Flange Size Is Critical
Using an incorrect flange size leads to discomfort and reduces the ability to remove milk efficiently. A poor fit causes friction or excessive pulling, which may result in pain, chafing, swelling, or cracking of the nipple tissue. Pain interferes with the hormones needed for milk flow, making the pumping session less productive.
The wrong size also compromises milk output efficiency, which is a concern for maintaining supply. If the flange is too small, the nipple cannot move freely, and milk flow is restricted. Conversely, a flange that is too large may pull in too much of the areola, compressing the milk ducts and leading to inefficient milk removal. Ineffective expression signals the body to produce less milk over time, decreasing overall supply.
Physiological Causes of Size Variation
Nipple size is dynamic, influenced by biological and temporal factors, meaning the correct flange size can change over weeks or months. A significant cause of initial variation is postpartum swelling, common in the days and weeks following birth. Swelling from IV fluids given during labor, combined with initial engorgement, can temporarily increase nipple and breast size.
As the body regulates and postpartum swelling subsides, the nipple diameter often decreases. Initial sizing should be checked around two weeks and then ten weeks postpartum once the milk supply is established. Hormonal fluctuations also play a role, as the highly vascular nipple tissue is responsive to changes throughout the menstrual cycle.
Overall tissue characteristics can change due to consistent pumping. Frequent and prolonged suction alters the elasticity and shape of the nipple over time. Temporary swelling can also occur if a flange is too large, causing fluid to accumulate in the nipple and artificially increasing the measured size.
How to Determine the Correct Flange Size
Determining the correct flange size begins with measuring the diameter of the nipple, excluding the areola. It is recommended to measure both nipples, as they may require different sizes for optimal comfort and performance. To get a starting measurement, gently stimulate the nipple to make it erect, then measure the diameter across the base in millimeters.
Once the nipple diameter is measured, a small allowance (typically two to four millimeters) is added to determine the appropriate flange size. For instance, a nipple measuring 17 millimeters suggests a starting flange size in the 19 to 21-millimeter range. This allowance ensures the nipple moves freely within the flange tunnel without painful rubbing.
The physical fit during a pumping session is the most important confirmation of correct sizing. With proper fit, the nipple should be centered in the tunnel and move gently back and forth without friction or pain. Only a minimal amount of the areola should be drawn into the tunnel, and the rhythmic tugging must be comfortable.
Signs of an incorrect fit indicate a need for re-measurement or a size change. If the flange is too small, the nipple will rub against the sides of the tunnel, causing pain, a white ring around the base, or nipple blanching. If the flange is too large, too much of the areola will be pulled in, leading to swelling or a bruised ring on the breast tissue outside the areola. If milk output decreases or pumping becomes painful, re-measuring and trying a different size is necessary.