Separating Your Milk

The amount of fat in your breast milk can vary during a pumping session and at different times of the day. If your baby doesn’t get enough fat, he or she may have trouble gaining weight.

If you are pumping more milk than your baby needs each day, you can increase the fat in your milk to help your baby grow.

Foremilk and hindmilk

The first milk that comes out of your breast during a pumping or feeding session is called “foremilk.” Foremilk is mostly water. It contains protein and other nutrients, but it is low in calories and fat.

As the breast is emptied, the amount of fat in the milk gets higher and the milk has more calories. The milk at the very end of a pumping or breastfeeding session is called “hindmilk."

You can separate your milk to collect milk that is higher in fat and calories. If you make lots of milk (more than 900 ml per day), or if you get a lot at one pumping (more than 200 ml), your milk might be watery. You may need to separate it to increase the fat.

It is helpful to know how much milk you get from each breast at each pumping session. You can plan to remove the first one-third that you pump. For example, if you normally pump 60 ml on each breast, you will remove 20 ml of foremilk. Foremilk can be frozen for later use.

Separating your milk

Follow these directions for separating your milk:

  • Have extra breast milk storage containers ready.
  • Begin pumping your breasts with the breast pump. About two minutes after the milk starts flowing steadily, turn the pump off, pour this milk into a separate container and label it “foremilk.” This should equal about one-third of the usual amount you pump.
  • Continue pumping until your milk flow stops, then for two more minutes. Label these bottles “hindmilk.”
  • Hindmilk can be fed to your baby to help him or her grow. You are an important part of your baby’s care.

You may have to separate your milk a few times before your baby's care team at CHOP determines which is the best milk to feed to your baby.

Testing the fat

Sometimes we need to know exactly how many calories your baby is getting. One way to do that is perform a creamatocrit test on your milk to measure the amount of fat and calories in the breast milk.

Generally, human milk contains about 20 calories per ounce, but the fat content can vary greatly throughout the day and during a single pumping session. To better understand the fat and calories of your breast milk, your nurse may ask you to save milk that you pumped at different times of the day so we can test it.

To test the milk, we place a small amount in tiny sealed glass tubes spin them for 3 minutes in a machine called a centrifuge. The spinning causes the cream in your milk to rise to the top of the tube. We can then compare the amount of cream to the rest of the milk in the tube. The amount of cream helps us to figure out the amount of fat and calories in your breast milk.

To learn more about how breast milk testing can help your child, see our new Human Milk Management Center.

Reviewed by Diane L. Spatz, PhD, RN-BC, FAAN on August 01, 2012