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Nipple size changes: What that means for pumping and flanges

Updated: Oct 12, 2021

by Ashton Fortin Higgins, PhD, MEd, CLC, ACS, certifying cALS

Baby registry time can be an exciting time for buying the essentials, like a breast pump. But knowing that nipple size changes and what means for buying a breast pump before I gave birth is a piece of information I wish I knew during pregnancy.

Why Should I Wait To Buy My Breast Pump?

One reason is because your nipple size will increase while pregnant. The potential up to 2.3mm was observed in one study. What does this mean? With all the extra blood flow, the potential to base your pump needs on what you need while pregnant may skew your decision making.


  • My nipple width measures 11mm before pregnancy. Then right before I give birth, it's up to 14mm. Typically, 14mm means we need a 16mm to 18mm flange.

  • But what if I get extra IV fluids during birth? I'm now swollen. Perhaps my nipple increases to 16mm to 17mm right after birth. Now my sizing needs have changed from 16mm to 18mm flange to a 18mm to 20mm flange.

  • What if on day 5 postpartum, the swelling has gone down? I'm measuring a 15mm, needing a 17mm to 19mm flange.

The sizing needs here have ranged from 16mm, 17mm, 18mm, 19mm, and 20mm. How do you know what breast pump to pick? Typically, we don't know at this point in the game (pregnancy) what size we will need.

Most main brand pumps do NOT have a wide range of small sizes.

Let me say it's a let down (no pun intended). You have your name brand pump at home ready to use and you need a size your pump doesn't offer. What the? Can't just run out to the store and get it. It's a problem. You are now waiting at least 24 hours with your amazon purchase to get the most appropriate size. There was a this ideology at one point that most standard sizes of flanges ranged in the 21mm to 30mm range---origin unknown. You needed to size up, which is not always the case. In fact, most studies (1,2,3) that have observed nipples indicate nipple diameter is much less than the need for a 20mm+ flange. They are ranging from 10.8mm in diameter to 15.9mm in diameter which indicates the need for more sizing needs in the teens not 20s. One study had a participant with 11mm use a 21mm flange. While maybe (big emphasis on maybe) one session or two with this too large flange can be tolerable, in no way should someone be using 10mm larger than their nipple diameter for long periods. Pumping with the wrong size can lead to inflammation, cracked and swollen nipples and aureoles. This is why pumping with the standard 24mm or 25mm can be a problem, especially long term like in exclusive pumping.

You could spend less money by waiting and buying a breast pump after giving birth.

You used a Symphony or a Platinum in hospital. Maybe you want to use some of those parts? Now you can tailor your needs of pumping with what each company offers. Will you need to be mobile? Will you need to pump on the go or often? Are you okay being plugged in for the amount of times you see yourself pumping? Did you plan on nursing, but now you find yourself in a situation where your little one is in the NICU and you need to pump during the middle of the night at home? You may find yourself nursing and only need to pump when away from baby. These are the types of questions that can play a role in your pump choice. It's also okay to choose a brand that's not available in store and only online. Breast pump technology has come a long way and you do not need to just settle for what's at the department store. Do remember if shipping is pricy to buy what you need + replacement parts ahead of time.

You could always buy inserts but you'll need to wait at least 24 hours.

Because nipple size can change throughout your pumping journey, you may find yourself just needing a size that isn't offered by your breast pump brand. This can happen months after you've been using you pump. Example, I've been using a 21mm flange and now I find myself needing a 19mm flange. Hard flanges made by brands other than the manufacturer and inserts are the quickest fixes. Disclaimer: Many pump companies will void warranties if you attempt to hack or use other brands' compatible parts. Inserts are helpful because they typically adapt to the flanges you have, but will often need to be purchased through Amazon. Some people suggest cutting them to make them work in certain pumps, but remember that cutting can have residue at the ends that may make their way into milk accidentally at any point, especially when they are constantly being sucked by the breast pump. I know that comfort is important but making informed decisions about breast pumps and sizing is important. If you need an insert, I recommend keeping it intact as you insert it into your flange to work with your pump. Luckily, there are now flanges out there to fit your Elvie & Willow without needed to cut anything (see below)! You can also seek a brand that makes the flange size you need. As a professional who is to uphold the IBLCE ethics and code of conduct, I cannot endorse a specific brand or breast pump. But I can provide you a list of companies that currently offer sizes in the teens (mm), in no particular order.

  • Maymom (Hard Flange only)

  • Fitme by Freemie (Insert)

  • Ruff and Tumble

  • Maymom (Hard Flange+Connector)

  • Maymom (Insert)

  • Maymom (Ameda Style)

  • Onatural

  • Momcozy

  • Pumping Pals

  • Lacteck

  • Pumpables

  • Liangzhi (Shorter inserts for Elvie & Willow option)

What about the prenatal flange sizing options?

These can be helpful for sure. Many nipples are not going to need the 24mm and 25mm flange, but it's the standard size that comes with most pumps. So even if your nipple is 15.9mm at the end of pregnancy, needing a 18mm, 19mm or 20mm flange is a better start then 24 or 25mm. Like any new size, there's a follow-up appointment, or should be. Ten to 14 days postpartum is the "sweet spot". If you do not end up being someone who needs a pump 24/7, you may be able to get by with hand expression for the occasional time you need to express until your nipple blood flow and your hormones slowly recover from childbirth. Around that 2 weeks postpartum mark you'll be ready for your first fitting. If you don't need to pump until you have to go back to work. Consider getting sized 2-3 weeks prior to the time you see yourself needing more pumping sessions.

However, if you are pumping 24/7 with a size that's too large, you are going to have nipple swelling and potentially nipple trauma. Here is the unfortunate news. Many LCs out there are "eye balling" sizing. Please note this is not their doing, it's just that pumps were once used as a an occasional device. The "it looks good" saying is because there is an assumption that there should be some space between the nipple and the flange canal. There is very little training on what that looks like to the naked eye. So if there is space "it looks good" is said. There's also one study that said flanges may fit small, and since then, it seems like size up is the motto. There will always be individuals who may truly need a larger size than 24mm/25mm, but for the majority we are sizing down. But here is the good news. It's 2021. Most trained lactation professionals (although not many) who excel in flange sizing offer it as a service. THEY CALL IT OUT! And once baby is here, there are options to get sized within 24-48 hours. It's mostly done virtually (including Pumped Love Lactation), and if you live in the Niagara Region, I include it in my initial assessment home visits. Imagine you have baby on a Sunday, you are sized by Monday and by Tuesday/Wednesday you are using the new size.

If you are asking yourself "But Sunday to Wednesday is long, how will I make due?" The first milk we make is syrupy, thick and yellow. It is called colostrum. It is much easier to get this milk out with hand expression than a breast pump. If you had a vaginal birth, in most cases your milk transitions to mature milk, the whitish milk, by day 3 (i.e. Wednesday). If you had a c-section, in most cases your milk transitions to mature milk by 5 to 7 days postpartum. Generally, inserts are the way to go because they will mostly likely adapt to the flange of the pump you will purchase when you've assessed your pumping needs. Ultimately, you can always be sized before having your little one, to eliminate any worries you have about being unprepared. The important thing to note is that the size of your nipple could change at birth, two weeks postpartum and at occasional times throughout your lactation journey.

Most exclusive pumpers have several pumps and pieces.

What tends to happen is you buy your pump before birth and maybe turn exclusive pumper. You'll soon find yourself wanting a goldilocks pump. This can lead into a search for different pumps to meet your needs to have exclusive pumping work for you and your family. An example is a pump for at home and a discreet pump for when you are out. Sometimes the pump you buy before birth isn't meant to be a used by an exclusive pumper. Some pumps are only good for so many hours, meaning it will need replacement more frequently. This is not always available for a free replacement. Some pump companies are more open about letting their customers know how many hours their pump motors are intended to work efficiently, some companies are not. Several pump pieces are key to ensuring you are not going to be without a piece at 2am when you need to pump.

You still feel like you are missing something if you don't have a pump available before giving birth.

I get it. You want to be prepared. My best suggestion is do some research. Find out which pumps have the most size options, including flange sizes between 15mm to 19mm, especially since evidence based nipple studies are saying we are ranging from 10mm to about 16mm in nipple diameter (12mm to 20mm in flange size). If you are really wanting a specific pump, make sure smaller flange sizes are available and other brand flanges that might be compatible. Reminder: Many pump companies will void warranties if you attempt to hack or use other brands' compatible parts. You can always size your nipples before birth, but it is in no way a sure thing to say it will stay the same at labour/delivery as well as throughout lactation. If you find yourself without a breast pump after the birth of your baby while in the hospital, you can ask to use their multi-user breast pump if you plan to exclusively pump or because the hospital believes it's currently required during your lactation journey. They will give you a personal pump kit and it is hygienic. Most hospitals offer to rent out these pumps and you can do so until you figure out the right pump for you. You can also contact your insurance provider to find out how long it takes to get the breast pump from the moment you make your choice to the moment you have it delivered.

Happy pumping!

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