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It seems like it should be so easy. Place the pump on your breasts, hit start, and your breast milk will just magically come out into little storage bottles or bags. How hard can it be, right?

Then, you open your pump kit only to find any number of parts to sanitize and fit together. If you’re like most new parents, at this point you start to wonder, what do all these parts even do?!?

Surveying all the different breast pump parts, your eyes will almost certainly be drawn to the oddly shaped shield designed to go over your breast. The instructions may refer to it as a flange, but how does it work and how is it supposed to fit?

If you’re confused and frustrated from trying to understand your breast pump (and potentially even in some pain from milk you need to express!) allow us to accompany you into the world of breast-pump fitting for all the answers you seek!

The flange is the part of the breast pump that comes in contact with your body when placed onto the breast and nipple, forming a vacuum seal with the areola. It’s shaped like a funnel.

Why is it necessary? Well, the flange draws your nipple into the tunnel of the pump where milk is extracted. The flange also helps to create necessary suction to extract milk by forming a seal.

Flanges are available in a wide range of sizes, which indicate the size of the smaller tube that pulls in the nipple on the narrow end of the flange. Depending on the pump you choose, flanges may also come in a variety of different materials, including hard plastic, silicone, or even glass.

This is important, because you need to find a flange that fits your breast comfortably. (Make sure to keep reading to find out how to determine your flange size, since a proper fitting is essential to successful pumping.)

When you purchase or rent a pump, they typically only come with one or two sizes of flanges. If you need another size flange (which many people do), you can order it from the pump manufacturer, Amazon, or other baby product stores.

You’ll want to make sure that whatever breast pump flange you might purchase is specific for your pump.

Because pumps are all designed differently, a flange designed for another pump is unlikely to fit with the rest of your system, which makes it useless. (At least useless for pumping. It might be a good bath toy though?)

Believe it or not, the process of finding the prefect breast pump flange can actually take a while and require testing several different sizes. It’s not quite perfect-pair-of-jeans level complexity, but it still takes a few steps.

Before you test out any flanges, you’ll want to check to see if your preferred breast pump has a measuring guide for flanges. Many manufacturers have their own specific guides, but if you can’t find one specific to your pump, you can go by the measurement in millimeters across the base of your nipple.

This detail is key. Keep in mind when measuring for your breast pump flange that the flange’s measurement is based on the diameter of the nipple where it meets the areola and not the areola itself. It’s an easy mistake to measure the areola and end up with a flange that is too wide.

Another common mistake is measuring the nipple at the tip instead of the base. Doing so may give you too small of a measurement and result in too tight of a flange.

This is a problem, because an ill-fitting flange will not suck the milk effectively and may leave a lot of milk in the breast. This can lead to poor milk production, discomfort, and infections.

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Even if you’ve measured everything perfectly, the final answer to knowing if you’ve found the right flange is going to come when you place it on your breast.

A flange fits correctly when:

  • your nipple is centered in the tube
  • no parts of your nipple rub against the sides
  • little or no areola is pulled in when the pump is turned on

On the other hand, a flange is not fitting properly when:

  • you experience nipple pain during or after the pumping session
  • you notice your nipple is becoming discolored, chapped, or otherwise injured

A pump that is suctioning your breast correctly will mimic how a baby would suck. Your nipple needs to be able to move in and out of the flange’s tunnel to do this.

If your nipple can’t complete this movement easily, it’s going to be injured by friction when the suction is turned on, and the pain is only going to get worse each time you pump.

After placing the flange on your breast, you’ll first want to check the flange’s fit without turning on the pump. Why? Well, once the pump has been turned on, if the flange does not fit properly the compression and rubbing can cause the nipple to swell and otherwise change shape.

After this happens, it can be really hard to find the right flange, so it’s best to wait until you’re fairly confident about the fit before hitting the power button on your pump.

Keep in mind that your breasts can continue to change their shape over time, as you go through pregnancy and even through the postpartum breastfeeding period.

So you may need to use several different flange sizes by the time your pumping journey is complete, says Nancy Mohrbacher, IBCLC, on her Breastfeeding Reporter Blog.

It’s important to have the right size flange, so that your nipple won’t rub, pinch, or be constricted in painful ways while you pump. Nipple damage and great pain can occur if your pump flange isn’t the right fit!

In addition to breast and nipple pain, using the wrong sized pump flange can negatively impact the amount of milk you are able to get out of your breast.

  • A flange that fits too tightly will cause the breast to be constricted in ways that can lead to clogged/blogged milk ducts. (When ducts are clogged, they don’t release milk and new milk isn’t formed as quickly.)
  • On the other hand, a flange that fits too loosely won’t provide adequate suction. This can also lead to milk being left in the breast and lower milk production in the future. Pain and infection can develop from this as well.

You’re not alone if you discover that finding the perfect flange for your breasts isn’t easy. If you’re having trouble finding the right fit, a lactation consultant or pumping specialty store might be able to help.

Because different brands of pumps have differently shaped flanges, you may discover that some pumps fit or work better with your body. Don’t be scared to try out different brands and sizes of flanges.

For most people, pumping is a learned skill that requires practice to master. (While studying how to put together you pump, you should also make sure you take the time to master hand expression and hands on pumping. You’ll be grateful you did!)

Pumping might seem easy in theory, but when you’re first using your pump you’ll probably realize you have a lot of questions.

A nurse, lactation consultant, doula, or knowledgeable friend can be an invaluable resource for you as you navigate putting your pump together and making sure everything fits properly.

It’s important to take good care of your breasts, so having pump parts that fit properly and don’t rub, pinch, or constrict your breast is a must.

You’ll also want to make sure that you’re following recommended guidelines for appropriate pumping frequency. Pumping too frequently or not removing enough milk can both be hard on your breasts.

Don’t hesitate to contact your doctor or a lactation specialist if something doesn’t seem right. Problems with milk production and expression are best handled right away, and finding the solutions can making your pumping experience far more successful.