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Mixing Breastmilk

Updated: Oct 9, 2023

New research on breastmilk

The world of breastmilk storage has gone a bit crazy this week. New comments from the AAP (American Academy of Pediatrics) have finally acknowledged what science and research has told us for a while now... that breastmilk has bacteria fighting qualities. Google it and you will find some pretty awesome images of breastmilk and bacteria in petri dishes, the breastmilk is definitely the superhero.

Lots of pumping mums have got very excited as they have now been told they can combine their milk from different pumping sessions, and that fresh milk can be added to older milk (within the same day of pumping). Sounds exciting, especially if you are an exclusively pumping mum with a busy schedule.

Here's the link to the research everyone is getting excited about >>>

So, has this changed any of the recommendations that I give to new parents?

Quick answer, NO. The protocols and procedures I recommend to all of my clients are based on:

  1. the stage you are at in your breastmilk journey (i.e. novices, at the beginning of building your supply)

  2. immature newborn little guts (that we don't want to introduce any bacteria too if we can avoid it)

  3. what information you can digest at this stage in parenthood (no offence, but simple instructions work best within the first month for most new parents)

  4. practical, easy, safe(est) steps

Anyone that has had me as their Postpartum Doula would have heard me say that it is OK to mix your breastmilk that you hand express, HaaKaa or pump on the same day, my only caveat is that I tell everyone to chill the milk to the same fridge temperature before mixing - the main reason for chilling is to stop/slow any bacteria growth that may be present.

Despite the science stating that breastmilk has bacteria fighting qualities, i really really really do not want my clients breastmilk fighting ANY bacteria, I don't want you to have to worry about ANYTHING during your fourth trimester. I want you to be totally stress free. So if that means we put the bottle, or bag, in the fridge to chill it for a little while, well, yeah, I'm going to suggest to do that.

With regard to pooling breastmilk, at Empowa, we have been advising to do this for a long time (at chilled fridge temperature), but we also say to do this with your babies stomach size in mind.

Below are three examples based on very different situations.

Many many new parents do not need to pump at all, so this is not a recommendation to start pumping, or a programme to follow, just examples of how to measure and store milk in different quantities based on different scenarios

1st day out of hospital

Dr advises you to give top up feeds for helping to clear jaundice

Mum is expressing 10ml per time

Mum is expressing 10 times per day (after each direct latch)

I recommend pooling the milk in 5 bags of 20mls

6 weeks out of hospital

Mum is pumping 80ml per pump

Mum is pumping 4 times per day (and direct latching 8 times)

I recommend pooling the milk in 4 bags of 80mls

6 months old

Mum is pumping 200+ml per pump

Mum is pumping 4 times a day (and direct latching 3 times)

I recommend pooling the milk in bags of 180-220mls depending on appetite and weaning stage

So why haven't I changed my recommendations for the majority of my clients?

The research paper that everyone is referring to was primarily done to ascertain a way to ensure that the calorific, and nutrient, content of every feed could be averaged out between 24 hours of expressed breastmilk, which is particularly useful for premature babies (I could do a whole other blog about how incredible it is that we produce breastmilk with different composition for each feed based on the time of day, activity etc, but I'll save that for another day). In the process of researching this they also tested a more convenient process of pooling fresh milk with previously pumped milk, and found little difference in bacterial content (with the same 24 hours) - note then that it wasn't the primary reason for the research.

Secondly, hygiene during the process of expression is still incredibly important, you would still not want to pool milk that has significantly high exposure to bacteria. So how you wash, sterilise and store your equipment is still very very important, and something that new parents are still getting used to. The updated advice may be exciting for exclusively pumping parents who are back to work, especially if they can now carry one large flask for storage purposes. BUT I urge a little caution as pumping at work often leads to hygiene short cuts with pumping equipment. If you are already gambling a little with the hygiene to save yourself some time, then I wouldn't also gamble with pooling; so you decide, is it quicker, or easier, to thoroughly wash your pump parts between each pump or chill your milk before pooling it?

For those that don't know what my simple storage process is for parents in the first few weeks, here's a quick explanation below.

Kathy's step by step storage guide for new parents the first few weeks at home

  1. First expression of the day: transfer the milk into a storage container (glass, silicone or plastic bottle or bag), place in the back of the fridge

  2. Second expression of the day: keep the milk (initially) in the expression container, place in the back of the fridge

  3. Third expression of the day: keep the milk (initially) in the expression container, place in the back of the fridge, now transfer the second expression into the first expression

  4. Fourth expression of the day: keep the milk (initially) in the expression container, place in the back of the fridge, now transfer the third expression into the previously pooled milk

  5. etc etc

  6. At the end of the day divide into storage bags or containers of no more than 30mls in the first week to avoid wastage

breast milk storage bags

I hope this article helped explain what all the fuss has been about, why some people are excited whilst some people, like me, are a bit "yeah, that's not life changing enough to get me excited yet". I love reading all the new research, my life is dedicated to it, and I will always try to give you practical evidence based advice.

As is always the case, please remember that as a Postpartum Doula I am an expert in the normal, not a specialist in the abnormal. I don't, and won't, give medical advice and nothing in this article, or on my website, should be deemed as such. Listen to your health care team and I'm happy to be a sounding board if you need one.


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