The 411 on Prenatal Flange Sizing
If you're planning to include pumping in your breastfeeding journey, getting the right flange size is not something you should leave until after birth. Prenatal flange sizing can set you up for success from day one, helping you maximize comfort, efficiency, and milk output while minimizing pain and complications.
But how do you find the right size when your body is constantly changing? What are the factors that influence flange fit? And how can you avoid common pitfalls in the early postpartum period?
This guide will walk you through everything you need to know about prenatal flange sizing, combining expert insights with practical strategies to help you make the best choice for your pumping journey.
What Is Prenatal Flange Sizing?
Prenatal flange sizing is the process of measuring and determining the optimal range of flange sizes for you before your baby arrives. Unlike traditional flange sizing, which happens after birth, prenatal sizing takes into account:
The natural changes in nipple size during pregnancy
The impact of fluid retention and postpartum swelling
Your individual nipple shape and elasticity
Any risk factors (such as preeclampsia, C-section, or IV fluids) that could temporarily affect sizing
Flange sizing is not a one-time measurement. Your nipple size will continue to change throughout pregnancy and postpartum, which is why we provide a range rather than a single, fixed size.
Why Is Prenatal Flange Sizing Important?
Many new parents don’t realize how much flange fit impacts milk supply, nipple health, and pumping comfort. Having the right size from the start offers several benefits:
✅ Optimizes Milk Supply – The first 10 to 14 days postpartum are critical for establishing your milk supply. Using a poorly fitting flange during this window can negatively affect stimulation and milk removal, leading to long-term supply issues.
✅ Prevents Nipple Damage – Too-small flanges can cause friction, blisters, and pain, while too-large flanges can lead to swelling and ineffective milk extraction.
✅ Reduces Pumping Discomfort – Pumping should not hurt! A properly sized flange minimizes discomfort and allows for more effective, pain-free pumping sessions.
✅ Helps You Prepare Ahead of Time – Rather than scrambling to adjust flange sizes while navigating postpartum recovery and newborn care, prenatal sizing allows you to enter this phase with confidence.
How Your Nipple Size Changes During Pregnancy & Postpartum
Understanding how nipple size fluctuates can help you plan for the right flange range. Here’s what to expect:
During Pregnancy:
Nipple growth begins early – One of the earliest signs of pregnancy can be a sudden increase in nipple size (by 2+ mm).
Steady increase throughout pregnancy – On average, nipples grow by several millimeters until around 36 to 38 weeks gestation (though for some, changes stabilize as early as 32 weeks).
Immediately Postpartum:
Biggest nipple size increase occurs right after birth due to postpartum swelling and fluid shifts.
If you received IV fluids, had a C-section, or required magnesium for preeclampsia, you may experience excessive swelling, requiring a slightly larger flange initially.
Nipple size will begin to decrease within the first two weeks postpartum as swelling resolves.
Long-Term Postpartum Trends:
Most parents experience a gradual decrease in nipple size over time.
If your nipple size suddenly increases weeks or months postpartum, we screen for changes in milk supply (such as correcting low supply issues).
Hormonal shifts (such as period return or weaning) can also impact nipple size.
How to Determine Your Prenatal Flange Size
1. Measure Around 36 Weeks Pregnant
The ideal time for prenatal flange sizing is between 36 and 38 weeks. This is when nipple size is usually most stable before birth. However, if you have a high-risk pregnancy or anticipate an early delivery, we may size you earlier.
2. Expect a Postpartum Size Range
Rather than one fixed size, we provide a range based on your measurement. For example, if you measure 17 mm at 36 weeks, we may recommend:
19-21 mm flanges for the immediate postpartum period
A plan to reassess and size down as swelling subsides
3. Consider Flange Shape & Material
Flange shape matters just as much as size! Some people need triangular, ball-shaped, or broad-based flanges depending on their nipple anatomy.
Additionally, silicone inserts vs. hard plastic flanges may feel different. If you’ve pumped before, consider your personal material preferences from past experience.
4. Use a Sizing Kit for Adjustability
We often recommend a flange insert kit (such as 13-21 mm) to give you flexibility in those first few weeks postpartum. These allow you to fine-tune your fit without purchasing multiple separate flange sizes.
When to Reassess Your Flange Size Postpartum
Since nipple size continues to change, it’s important to check your flange fit regularly:
📌 3-5 days postpartum (especially if you had significant swelling)
📌 10-14 days postpartum (a key check-in as initial swelling resolves)
📌 6 weeks postpartum (when supply and nipple size stabilize further)
📌 12 weeks postpartum
📌 Every 3 months postpartum or when your period returns
If you're experiencing pain, nipple damage, or changes in supply, get reassessed sooner!
Common Myths About Prenatal Flange Sizing
🚫 "Your nipple size stays the same postpartum."
❌ False! Nipple size typically decreases after birth, especially after initial swelling resolves.
🚫 "You can pick one flange size and stick with it."
❌ Not true! Most people need to size down in the first few weeks postpartum.
🚫 "All flanges are the same."
❌ Nope! Flange shape and material also impact fit and effectiveness.
🚫 "You can DIY flange sizing without support."
❌ While some online calculators exist, professional guidance can help you avoid common mistakes and optimize your fit.
Final Thoughts: Is Prenatal Flange Sizing Right for You?
If you plan to pump—whether exclusively or occasionally—prenatal flange sizing can be a game-changer. It helps you start your postpartum journey with the right tools, reducing discomfort and maximizing milk supply from day one.
At Genuine Lactation, we offer personalized prenatal flange sizing to help you find the best fit based on your unique needs, pregnancy history, and postpartum risk factors. We also provide ongoing support to adjust your flange size as needed, so you can focus on your baby without the stress of pump discomfort or supply struggles.
💡 Want to get sized before your baby arrives? Book a prenatal flange sizing session with us today!
Got questions? Drop them in the comments below or reach out—we’re here to help!
