Making breast milk: does boob size matter?

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The joke used to be that I could get into a stag party wearing a singlet and nobody would notice I was actually a girl. I was an A cup desperate to be bigger, but as a teenager influenced by media images of buxom , full-busted women, the boob fairy seemed to have passed me by.  Back then, I didn't care about the function of breasts, aka breastfeeding. I just would have liked to have a 'pair'.

Pregnancy made a few changes to my tiny boobs and when my baby was born, I woke one morning to breasts that seemed as though they couldn't possibly belong to me. I had grown boobs overnight! Apart from the pain, I thought, if this is what breastfeeding does, count me in.

I of course knew that breastfeeding was the healthy choice for my baby, so I wasn't only motivated by the promise of finally filling a bikini top … although it certainly felt like a bonus! 

Breastfeeding didn't come so easily with that first baby. He fed every couple of hours day and night for months, and when the health nurse asked "how many feeds a day?" I must have looked confused. She then asked, "Has he dropped any feeds?" "Ummm … maybe he's gone from 24 to 20?"

Thankfully, this good woman had just returned from a stint in New Guinea where women didn't watch clocks and babies were almost constantly attached to their mothers' breasts; my baby was happy and thriving so my nurse didn't question my milk supply. 

Although everyone around me seemed to have their babies in a routine – even bathing their babies daily before the 6am feed – it didn't make sense to me to stretch out breaks between meals for a hungry baby, so I pretty much fed him and loved him and he grew. Because the women around me were also formula feeding, I consoled myself that breast milk digested more quickly than the formula, so it seemed natural that my baby would feed more often. My ignorance was blissful and my baby thrived.

Different storage for different women

We now know that women have different breast milk storage capacities – a woman like me, with a smaller storage capacity, will need to feed her baby more frequently than a woman with a larger one. Ultrasound studies by Dr Peter Hartmann and team at the University of Western Australia have shown that although healthy breastfeeding women produce similar amounts of milk over a 24-hour period, breast milk storage capacity can vary up to three times as much between individual women. But this isn't necessarily related to breast size and doesn't influence milk production ability: a smaller breasted woman may have a good supply of glandular tissue and less fat, which will mean a better storage capacity, while a larger breasted woman may have more fat in her breasts and less glandular tissue, and therefore have a smaller storage capacity.

I've met mums like Katie, who describes her breasts as changing from the size of half a lime to oranges while breastfeeding – she has a great supply and a good storage capacity despite smaller breasts. There's Coby, who has "rock melons" (medium to large breasts) – she initially struggled with low supply but with medication now has a supply that she says is "just right" for her four-month-old.  Then there are mums like Vicki, who has big breasts and a big supply that meets the needs of her twins.


What this all means is that while some women with a larger storage capacity will be able to feed their babies enough to go three or four hours between feeds (providing their baby has a big enough stomach – newborn stomachs are tiny!), other women will need to feed their babies more often. For women with a smaller storage capacity, a three or four hourly feeding schedule could result in a hungry, unsettled baby and a mother who questions her ability to produce enough milk. 

Instead of becoming stressed about how much milk your breasts are making or storing, I joke that we have either shot glasses or 'jugs'. You can drink a litre of water from a large mug or a smaller cup; if you're drinking from a smaller cup, you'll simply need more refills.  This means that if you breastfeed your baby according to his hunger signals, you'll never need to worry about your milk storage capacity.

Milk production works on a supply and demand basis. According to Dr Hartmann's research, an empty breast will make milk more quickly than a full breast, so milk production will speed up or slow down according to how hungry your baby is and how well he empties your breasts. If your baby doesn't drain your breasts or you space out feeds to allow your breasts to 'fill up', your hormonal processes will signal your breasts to make less milk.

The conditions that make it harder

While size generally doesn't matter, there are some medical conditions that can impact milk supply regardless of breast size, and for a small number of women, size and shape can be an indicator that there could be challenges to milk supply. For these women, there may be little or no breast development during puberty, and a lack of breast changes during pregnancy or when their baby is born. This can impact milk supply if they have a condition called mammary hypoplasia or insufficient glandular tissue (IGT).  

A study of 34 mums with breast hypoplasia concluded that other markers of this condition include: widely spaced breasts (breasts are more than 1.5 inches apart), breast asymmetry (one breast is significantly larger than the other), the presence of stretch marks on the breasts, an absence of breast growth (either during puberty or in pregnancy), and tubular breast shape ("empty sac" appearance).  

According to lactation consultant Diana Cassar-Uhl, "The unfortunate reality of hypoplasia is that although it is often easy to recognize in hindsight, the first clue that a mother has insufficient glandular tissue is usually primary lactation failure; her body simply does not produce milk. Even when everything else is in place for a good start to breastfeeding, the milk does not 'come in' or is not enough to sustain her baby." This can be devastating for a mother who wants desperately to breastfeed her baby but has to adjust her goals.

Maria, who has IGT, contacted me during her second pregnancy after a disappointing experience with her first baby. Together we made a breastfeeding plan which included lots of support, skin to skin resting with her baby as milk supply was established, donor milk screened and ready in case she needed to supplement, a nursing supplementer device (SNS), galactagogues (lactogenic foods plus appropriate safe herbals based on her medical history), and a postnatal visit scheduled to check on her feeding. Maria's baby is now six months old and this time around, albeit with supplementary feeds as necessary, she is still a breastfeeding mother – despite the size of her breasts.

Pinky McKay is an Internationally Certified Lactation Consultant (IBCLC) and best-selling baby-care author. She is the creator of Boobie Bikkies, all natural and organic cookies to boost your energy and support a healthy breast milk supply. Download Pinky's free ebook, Making More Mummy Milk, Naturally.