(Updated 10/28/21)

Flange sizing ALWAYS matters, but good flange sizing is especially important with wearable pump options.

Wearable pumps include full pump systems that fit in your bra without tubing like Willow Pump, Elvie Pump, and the newer Momcozy style pumps. It also includes wearable cups that act as a combined flange and milk container attached to a more traditional pump like the Freemie Cups, Spectra (CaraCups) Cups, Youha Cups, and the new Legendairy Collection Cups.

With traditional pump flanges, we can visualize the nipple while pumping, move the flanges around easily when necessary, and suction can be maintained even with a poorly fitted flange because it is manually held in place by your hands or a strong hands free bra. It's easy to see something is off before milk supply is compromised and nipple damage occurs.

With a wearable pump, we don't have the luxury of visualizing the nipple while pumping, and the ability of the pumps to function with poorly fitted flanges is less.

Poorly fitted flanges make the pump motor work harder to maintain the suction needed to express your milk (i.e. you keep having to turn up the suction and make the motor work harder which shortens it's life span.
Poorly fitted flanges allow opportunity for your flanges to slip out of place and compromise milk output and increase risk of nipple damage.
With wearable pumps, we don't always know the pump session was ineffective until the end of the session which risks future milk supply and increases your frustration with pumping.
The Elvie wearable pump has holes in the flanges known to cut the nipples when the tissue rubs, and excessively swollen nipple tissue is more prone to this type of damage.

Another factor in wearable pumps to consider is the motors commonly used for wearable pumps are not as robust as a heavy duty double electric breast pump, which can compensate for poorly fitted flanges based on the strength of the suction. What you can get away with with your Spectra or Medela pump is vastly different than the flange sizing tolerance the majority of people are tolerating with wearable pumps.

Here is a video I was able to get while Pressure Testing accessories with the Elvie Stride. When there was an air leak, the pump dropped suction and lost the ability to move milk, but once the air seal was restored, function resumed. Watch the numbers on the gauge to see how the lack of an air seal dropped the pump below the 200 mmHg threshold for functional pumping - only to be restored again to 275 mmHg which makes this wearable pump as strong as most well respected pumps on the market.

Pressure Testing the Elvie Stride and showing why an air seal matters © Genuine Lactation

So how should your pump flange fit?

This depends on the Wearable Pump option you are using:

With the exception of the Willow Pump, all other wearable pumps use the standard flange sizing goals which is between 2-4 mm from your pre-pump size. Where you fall in that range depends on a combination of your nipple elasticity, nipple shape, and the available flange sizes and styles in your ideal range.

With the Willow Pump, we want a slightly tighter flange fit to protect the areola from being damaged by the unique suction of the Willow Pump. Willow Pump uses constant suction which places the nipple and areola under increased pressure as compared to a traditional pump. This increases the risk of pain and nipple damage substantially, and very people can use traditional flange sizing ranges with the Willow Pump long term without causing trauma to the nipple, areola, as well as the sensitive milk ducts in that area. The majority of people find success with the Willow Pump using 0-1 mm from their pre-pump measurement.

What about the people who say they are just fine using much larger flanges with their traditional pumps?

Many of my clients have come to me frustrated that they were pumping comfortably and effectively with their traditional flanges at sizes 8-10 mm bigger than their pre-pump measurement, only to find wearable pumps were painful, ineffective, and nipple damage was resulting from using Wearable Pumps with the same flange sizing. These issues resolved when we sized down with the traditional pumps (which can cause low level damage that is agitated by the pressure of the wearable pump against the breast when used with these excessively large flanges even though it is not detected with these traditional setups) and then properly size the wearable pump options.

Why do these recommendations vary from other recommendations online or from the pump manufacturers themselves?

My recommendations absolutely vary from commonly presented recommendations, because in my clinical practice, I have found these recommendations to be outdated, inapplicable to modern wearable options, and they prevent clients from achieving comfortable and effective pumping. Therefore, I recommend what I have found to be effective in my clinical practice based on data I tracked about what allowed my clients to meet their goals. It’s always a client’s choice to choose the recommendations they want to try, but if you are frustrated with your pumping situation, why not give my method a try and experience a better pumping journey for yourself!

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