Breast Pump Flange Fitting Assessment Explained

A breast pump flange fitting assessment is not simply a matter of matching a number to a nipple measurement. It is a skilled, individualised review of how the breast, nipple, pump and feeding plan work together. For some families, a small adjustment may make expressing more comfortable or effective. For others, flange fit is only one part of a wider picture that may include pump settings, frequency of expression, milk supply, infant feeding, nipple trauma or the practical realities of family life.

Pumping can support many different feeding journeys: expressing for a premature or unwell baby, returning to work, combination feeding, managing temporary separation, donating milk, or feeding directly at the breast alongside occasional expression. There is no single ‘right’ pumping pattern, and there is no one flange size that is correct for every person.

What is a breast pump flange fitting assessment?

A flange, sometimes called a breast shield, is the funnel-shaped part of a pump that sits against the breast. Its tunnel is designed to allow the nipple to move during expression while the flange maintains a seal against the breast.

A breast pump flange fitting assessment considers more than the diameter of the tunnel. It brings together the person’s account of comfort and symptoms, observation of nipple movement during pumping, the amount of areolar tissue drawn into the tunnel, skin colour changes, the seal against the breast and the person’s response to the pump settings. It should also consider whether milk is being expressed in a way that is workable and sustainable for that family.

This matters because breasts and nipples are dynamic tissues. Nipple dimensions can alter during pumping and across the day. The anatomy of the lactating breast also varies considerably between individuals, so a measurement taken before pumping cannot, by itself, confirm an effective or comfortable fit (Ramsay et al., 2005).

Why Flange Shape and Size Matter

The findings from the Flange FITS™ study, published in 2025, highlight just how important individual flange sizing can be. While 24 mm remains a common “standard” size supplied with many breast pumps, participants in the study frequently needed considerably smaller flanges when sized according to their nipple measurement. The most commonly selected smaller-fit sizes were 15 mm and 17 mm. Participants also reported greater comfort and, on average, higher milk output when using the smaller-fit flanges. This is a useful reminder that there really is no “one size fits all” when it comes to breast pump flanges — and that the 24 mm flange supplied with your pump is simply a starting point, not necessarily the right size for you.

As a flange fitter, I look beyond the diameter of the tunnel. Flange shape matters too. Two flanges can have exactly the same tunnel diameter but feel and perform very differently because their overall shape, depth, angle and breast contact are different.

Maymom is one of the most commonly used flange brands among UK flange fitters, and it is the brand I suggest most often because it has one of the largest ranges of flange shapes available. Maymom has five different shapes, giving me much more flexibility when fitting a parent than simply being able to change the tunnel diameter. I use all five shapes, because different breast shapes and different levels of breast fullness can require very different flange designs.

Breast shape can make a real difference to how a flange sits. A softer, less full breast may sit very differently within a flange from a breast that is naturally fuller or more rounded. Then there is engorgement, when the breast can become considerably firmer and fuller and the tissue around the nipple can change shape. A flange that looks and feels right when your breast is soft may therefore not be the most comfortable or effective choice when you are very full or engorged.

This is why, when I fit a flange, I am looking at much more than a nipple measurement. I consider the size and shape of the nipple, the shape of the breast, how much breast tissue sits within the flange, how full the breast is, and what happens once the pump is switched on. The aim is for the nipple to move freely within the tunnel without unnecessary rubbing or compression, while the flange itself sits comfortably against the breast.

Material is another part of the fitting process. In my experience, most women respond better to a rigid, hard-plastic flange, as it provides a stable and consistent shape against the breast during pumping. Silicone flanges are softer and more flexible, which can be helpful for some parents, but softer does not automatically mean a better fit.

Ultimately, flange fitting isn't simply about finding the right number. Size, shape and material all matter, and so does the state of your breast at the time you are pumping. Your breasts can change considerably during your breastfeeding journey — and sometimes even during the same day. The flange that works beautifully for you at one point may not be the flange that works best when you are engorged, when your breast has softened, or as your body changes over time.

Why discomfort is not always a flange-size problem

Pain while expressing deserves attention, but it does not automatically mean that a flange is too large or too small. Excessive vacuum, a pumping session that is too long, friction from dry skin, swelling, engorgement, pump position, damaged components, infection, dermatitis or vasospasm may all contribute. A person may also find pumping uncomfortable despite a reasonable visual fit, particularly where there is existing nipple trauma or sensitivity.

Likewise, milk volume during a single session is not a reliable test of flange fit. Output can be influenced by the interval since the previous milk removal, stage of lactation, stress, hydration, pump effectiveness, breast storage capacity, settings and the individual’s milk ejection reflex. A low volume may warrant skilled support, but it should not be assumed to prove a poor fit or inadequate supply.

The available evidence on methods of milk expression shows that research is heterogeneous and that outcomes can be shaped by the context in which pumping takes place (Becker, Smith and Cooney, 2016). There is not currently a universally accepted, independently validated clinical standard that can determine an ideal flange size for every pumping parent. This makes careful assessment, review and shared decision-making particularly valuable.

What a careful flange fitting assessment may include

A clinician will usually begin by listening. Understanding why someone is pumping, how often they express, which pump they use and what they are experiencing is essential. A parent who pumps once a week for occasional separation may have different priorities from someone who is exclusively expressing for a newborn.

The assessment may include a respectful observation of a pumping session, with consent. This allows the practitioner to consider the flange’s position, whether the nipple appears to move freely in the tunnel and whether there is rubbing, marked pulling of surrounding tissue, persistent blanching, swelling or pain. The person’s own sensory experience matters as much as what can be seen.

Measurements can be useful as one starting point, especially when selecting flanges to try. However, they should not be treated as a prescription. The aim is not to achieve a particular appearance based on a photograph or a rigid rule about how much areola should enter the tunnel. Instead, it is to identify an option that supports comfort, effective expression where possible and skin wellbeing.

A meaningful assessment also looks at pump settings. More suction is not necessarily better. The highest comfortable setting is not always the most useful setting, and a lower setting may be more tolerable and productive for some people. Changes should be made gradually, with attention to comfort during and after the session.

Signs that a review may be helpful

Some early sensitivity when beginning to pump can occur, but ongoing pain, damaged skin or symptoms that continue after pumping are not something a parent should feel they simply have to endure. A review may be helpful where there is persistent rubbing, a pinching sensation, nipple blanching or purple discolouration, pronounced swelling, repeated milk leakage around the flange, or uncertainty about whether the pump is removing milk comfortably.

It is also sensible to seek timely clinical advice for breast redness, a hot or painful area, fever, flu-like symptoms, a breast lump that does not settle, broken skin with increasing pain, or concerns about milk supply and infant feeding. These symptoms have a range of possible causes and should not be managed solely by changing flange size.

For a baby who is feeding at the breast, an assessment should remain wider than the pump. Observing feeding, considering milk transfer and growth, reviewing maternal comfort and listening to the family’s concerns can help avoid reducing a complex feeding relationship to one piece of equipment. Anatomy provides information; function provides context.

Additional Tips for Getting More From Your Pump

Getting the right flange fit is an important part of pumping, but it isn't the only factor that can influence how much milk you express. If you're trying to improve your pumping output, there are several other things worth considering.

Heat and cold therapy

Warmth can be useful before or during pumping. A warm compress or warm shower may help you relax and can encourage milk ejection, and research into methods of expressing milk has found that warming the breast before expression can be associated with greater volumes of milk expressed. Gentle warmth can therefore be particularly useful if you find that your milk takes a while to start flowing.

Cold has a different purpose. A cool or cold compress can help reduce swelling, inflammation and discomfort, particularly when breasts are very full or engorged. Cold is generally more appropriate for reducing inflammation than trying to use heat continuously. If you have significant breast pain, redness, swelling or flu-like symptoms, seek appropriate medical advice rather than relying on heat or cold therapy alone. Current mastitis guidance also cautions against deep breast massage and excessive attempts to 'empty' the breast.

'Hands-on' pumping

Your pump does not have to do all the work. Hands-on pumping combines mechanical pumping with gentle breast massage, compression and hand expression. Research by Morton and colleagues found that combining hand techniques with electric pumping increased milk production in mothers of preterm infants.

This can be particularly useful towards the end of a pumping session, when the flow has slowed. Rather than increasing the suction, try gently compressing different areas of the breast while pumping, following the natural shape of the breast and avoiding painful or forceful pressure. You can also finish with some hand expression to remove milk that the pump may not have reached as effectively.

Breast stimulation matters

Milk production is fundamentally a supply-and-demand process. The more effectively and regularly milk is removed, the stronger the signal to the breast to continue producing milk. This is why the frequency and effectiveness of milk removal are so important when trying to build or maintain your milk supply.

There is an important difference, however, between feeding directly at the breast and expressing with a pump. Direct breastfeeding is a highly sensory and hormonal process. Your baby's suckling, touch, smell, sight and even the anticipation of a feed can contribute to the hormonal responses involved in milk production and milk ejection. Pumping is a more mechanical form of milk removal. It still provides nipple stimulation and milk removal and therefore still stimulates hormonal pathways, but it doesn't necessarily provide all of the same sensory stimulation as feeding your baby directly.

This is one reason some parents find it helpful to incorporate additional stimulation when pumping. Looking at your baby, smelling a piece of their clothing, having skin-to-skin contact, gently stimulating or massaging the breast before pumping, or simply taking a few moments to relax can all help create a more favourable environment for milk ejection. Oxytocin is particularly important for the milk-ejection reflex, and positive touch, relaxation and skin-to-skin contact can support the release of oxytocin.

So, if pumping feels very different from feeding your baby at the breast, you're not imagining it. The pump is removing milk mechanically, but you can add some of the sensory cues that naturally accompany breastfeeding. Combined with effective and regular milk removal, these can help support the process of expressing milk.

Galactagogues: natural and prescribed

You may also hear about galactagogues — substances used with the aim of increasing milk production. These include herbal products and prescription medicines. It is important to understand that a galactagogue isn't a substitute for effective milk removal. If milk is not being removed frequently or effectively, increasing prolactin alone will not necessarily solve the underlying problem.

Herbal galactagogues such as fenugreek, blessed thistle and others are widely discussed, but the evidence for many of these products is limited, and 'natural' does not automatically mean safe. Products can have side effects, interact with medicines and vary considerably in dose and quality. The Academy of Breastfeeding Medicine recommends addressing potentially correctable causes of low milk production and optimising milk removal before considering a galactagogue.

In the UK, domperidone is sometimes prescribed off-label for low milk supply following an appropriate assessment and after non-medical measures have been tried. The NHS Specialist Pharmacy Service identifies domperidone as the preferred medicine when drug treatment is considered, but also stresses that the evidence is limited and that treatment should be reviewed. It should only be taken under the direction of an appropriately qualified prescriber.

For me, the key message is that galactagogues should be considered as one possible part of a wider plan — not as a quick fix. Before reaching for a supplement or medication, it is worth looking at the fundamentals: is milk being removed often enough, is it being removed effectively, is the flange correctly fitted, and is the pumping process allowing you to achieve good milk ejection?

Don't forget the small pump parts

If your flange fit is good but your pump suddenly doesn't seem to be performing as well, don't forget to check the small parts of your pump. Valves, membranes and other silicone components are working parts of the pumping system and can wear over time. A valve that is stretched, damaged or no longer sealing properly can affect suction and milk removal, while a worn membrane can also affect the performance of some pumps.

These parts don't always need replacing at exactly the same interval for every pump. Check your pump manufacturer's guidance for how often valves and membranes should be replaced, but also look at the parts themselves. If a valve or membrane looks stretched, split, warped, cloudy, damaged or no longer sits correctly, it is worth replacing it. Parents who pump frequently may find that these parts need replacing more often than someone who pumps occasionally.

It is an easy thing to overlook: before assuming your body, your flange or your milk supply has changed, make sure your pump is still working as it should. A good flange fit cannot compensate for a worn or damaged pump part.

Sometimes the answer isn't that you need to pump harder. You may simply need to make pumping work better for your body.

Practical preparation for an assessment

It can help to bring the pump, the flanges currently in use and any parts that affect fit, such as inserts or collection bottles. If possible, note how long each session lasts, typical settings, frequency of pumping, pain or skin changes, and any patterns in milk expression. These details allow the discussion to focus on what is happening in real life rather than an isolated measurement.

Avoid making several major changes at once. If a new flange or setting is tried, allow enough time to notice comfort, nipple condition and how manageable the routine feels, unless pain or skin damage means it should be stopped sooner. Keeping changes measured makes it easier to understand what has helped.

A flange fitting assessment should leave a family with clear, realistic next steps. This may include trying an alternative size or shape, adjusting positioning or settings, checking pump parts, arranging feeding support, or seeking medical review. Sometimes the most helpful outcome is reassurance that fit appears reasonable and that another factor deserves attention.

A supportive next step

Pumping is often treated as a purely technical task, yet it takes place within a demanding period of recovery, caring and feeding. A thoughtful assessment makes space for both the practical and emotional aspects: what feels comfortable, what is achievable, and what will best support your family’s own feeding goals. If expressing is painful, stressful or simply not working as expected, you deserve to be heard and supported without judgement.

If you would like personalised support, you can visit tongue-tie.info to book a flange fitting. Together, we can look at your individual flange size, shape and fit, how your breast responds during pumping, and any other factors that may be affecting your comfort or milk removal. The aim isn't simply to find a smaller or larger flange — it is to find what works best for you.

References

Anders, L.A., Frem, J.M. and McCoy, T.P. (2025) ‘Flange Size Matters: A Comparative Pilot Study of the Flange FITS™ Guide Versus Traditional Sizing Methods’, Journal of Human Lactation, 41(1), pp. 54–64. doi: 10.1177/08903344241296036

Academy of Breastfeeding Medicine (2018) ‘ABM Clinical Protocol #9: Use of Galactogogues in Initiating or Augmenting Maternal Milk Production, Second Revision 2018’, Breastfeeding Medicine, 13(5), pp. 307–314. doi: 10.1089/bfm.2018.29092.wjb.

Becker, G.E., Smith, H.A. and Cooney, F. (2016) ‘Methods of milk expression for lactating women’, Cochrane Database of Systematic Reviews, 9, CD006170.

Morton, J., Hall, J.Y., Wong, R.J., Thairu, L., Benitz, W.E. and Rhine, W.D. (2009) ‘Combining hand techniques with electric pumping increases milk production in mothers of preterm infants’, Journal of Perinatology, 29(11), pp. 757–764. doi: 10.1038/jp.2009.87.

Mitchell, K.B. et al. (2022) ‘Academy of Breastfeeding Medicine Clinical Protocol #36: The Mastitis Spectrum, Revised 2022’, Breastfeeding Medicine, 17(5), pp. 360–376. doi: 10.1089/bfm.2022.29207.kbm.

NICE (2021) Postnatal care, NG194. Recommendation 1.5.12

Ramsay, D.T., Kent, J.C., Owens, R.A. and Hartmann, P.E. (2005) ‘Ultrasound imaging of milk ejection in the breast of lactating women’, Pediatrics, 115(2), pp. 361-367.

World Health Organization (2016) ‘Methods of milk expression for lactating women’. WHO e-Library of Evidence for Nutrition Actions (eLENA). Specialist Pharmacy Service (2024) ‘Using domperidone for low milk supply’. 21 June.

World Health Organization (2017) Guideline: Protecting, Promoting and Supporting Breastfeeding in Facilities Providing Maternity and Newborn Services. Geneva: World Health Organization.