There are several reasons that a breastfeeding mum might choose to introduce a bottle to her baby; for some, it is because they like the freedom of leaving a bottle of expressed milk when they go out, while others may be headed back to the workplace. Whatever their reason for wanting to use a bottle of expressed milk, it is important to do so safely.

How to express milk

Milk removal is the most important factor in milk production once your body is in the supply/demand phase of breastfeeding, so we want to ensure that the demand is appropriate. This means expressing milk to keep up with the baby’s demands while you’re not with them, but it also means not over-expressing milk and stocking your freezer unnecessarily, as this can lead to an uncomfortable oversupply.

Most women find an electric pump to be the most effective tool for expressing milk, but there are some who get a better yield from a manual pump or even hand-expressing. So, experiment a little, and then stick with whatever works best for you!

When you express milk with any pump or with your hands, it can take a minute or two to cause a release of milk. Then there will be some sprays of milk. These sprays will subside after a minute or so (this is a letdown). If you continue pumping, you will see fresh sprays arriving shortly. A pumping session will likely have several letdowns. If you are double pumping, just keep the pump in place for the full session. If you are single-pumping, you will get the best yield if you switch breasts each time you finish a letdown. Keep going back and forth between sides (or keep double pumping) until the first one of the following happens:

You no longer get sprays or drips from either side.
You have as much milk as you intended to pump.
You’ve been pumping for 15–20 minutes.

Remember that 8 short pumping sessions are more effective than 4 longer sessions. If you only have 5 minutes spare, then it’s fine to do a “quickie” pump session.

How much milk does your baby need?

The good answer is that it’s probably less than you think! Babies need increasing volumes of milk as they grow, until they reach their maximum milk needs at around 6–8 weeks. This volume then stays constant until milk volumes reduce due to the introduction of solids. Make sure you are using a baby-led bottle-feeding method to help prevent overfeeding. (See episode 25 of this package for baby-led bottle feeding.)

Before 6–8 weeks: A good rule of thumb here is that they need a total of 150 mL per kg body weight every 24 hours. So, for example, if your baby currently weighs 4 kg, they would need 600 ml of milk every 24 hours. If they are having 8 feeds (on average), we would expect them to drink around 75 ml of milk for each feed. These volumes can vary by around 20%, as we sometimes have a snack and sometimes a feast!
Between 8 weeks and 6 months: At this age, babies tend to take approximately 750-1000 ml every 24 hours. Again, assuming they are still having 8 feeds per day (which would be typical of a breastfed baby), individual feed volumes would be around 95–125 mL. Of course, if they are having more feeds per day, feed volume would be lower, and if they were having more feeds per day, it would be higher.
After 6 months, once solids have been established, the total milk volume taken in tends to go down. However, portion size would be similar to those you’ve established in the first 6 months, with the change being the number of portions taken per day. Be guided in volume by how much your baby has typically taken until now. If they’ve not had expressed milk until this point, try offering 120 ml and go from there.

How to store expressed milk

Often, you don’t use expressed milk right away but need to store it until it is needed. This chart explains how (and for how long) you can store milk in various conditions:

Type of milk/conditions	Ideal Temperature	Length of storage
Freshly expressed milk
Warm room	27-32°C	3-4 hours
Standard room	16-26°C	4-8 hours (err on the side of caution if room temp is at the upper end of range)
Insulated cooler with ice packs	15°C	24 hours
Refrigerated milk
Fresh milk	4°C	Up to a week
Thawed milk	4°C	24 hours
Frozen milk
Freezer compartment within fridge	Varies	2 weeks
Freezer unit within fridge/freezer	<0°C	6 months
Stand alone deep freezer	-18°C	12 months

These guidelines relate to feeding a healthy, full-term baby. If you have a premature or seriously ill baby, speak to your baby’s doctor regarding stricter storage guidelines.

How to thaw frozen milk

Ideally, if you know in advance that you will need the milk, you can thaw it slowly in the fridge. This usually takes around 12 hours.
Once defrosted, keep in the fridge and use within 24 hours. Do not refreeze.

How to warm milk from the fridge

Place the bottle or storage bag of milk in a cup of warm (not boiling) water.
Alternatively, use a bottle-warming device.
Never heat the milk in the microwave!

Things to note

The fat layer in stored milk will separate and rise to the top. Once warmed, gently swirl the milk, and it will reintegrate within the feed.
Unfinished bottles can be kept and offered again to the baby within the next 2 hours.
Spoiled milk will smell bad and taste sour.

How should I express and store my breastmilk?

Get the best advice on expressing and storing breastmilk from Unii Expert Wendy Lever.