Breastfeeding, Pumping, and Night vs. Day Milk: Your Questions Answered

When and for how long should I be pumping? Night vs. day milk? How long can breast milk stay at room temp, in the fridge, in the freezer?

When and for how long should I be pumping? 

Moms may pump for many reasons: engorgement, sore nipples or problems latching on; babies that are too sick or too premature to nurse; to increase or maintain milk production; to be ready for an occasional separation; so Dad can give a bottles; to go back to work; or personal preference.

Often the best time to pump is right after one, two, or three of the first breastfeeding sessions of the day. If your baby goes a long stretch without nursing, during their sleep or your work, pumping in-between nursing can be great.

Night vs day milk — does it make a difference whether I pump during the day or at night?

As it turns out, yes! Scientists in Israel have discovered that there is a circadian change in melatonin levels in breast milk. Melatonin is naturally produced by our bodies when it’s time for bed, to make us drowsy. Daytime milk has less melatonin, nighttime milk has more to help baby relax and sleep.

What does this mean for pumping? Well, one idea is to label the time of pumping on each portion of expressed breast milk. Pulling out a night-pumped portion for nighttime feedings could be just the ticket to a better night’s sleep. It might be a great trick for traveling with babies on long trips, too.

How long can breast milk stay at room temp, in the fridge, in the freezer?

I prefer keeping pumped milk in a cooler with an ice pack rather than storing it at room temperature, though in a pinch keeping it as long as 10 hours at room temperature can be okay.

In the fridge breast milk stays good from 3 to 8 days. If it’s not used within 72 hours, I prefer moving it to the freezer for extra safety. In the freezer, it stays good for 3 to 6 months (use your oldest milk first) and in deep freeze it stays good for an entire year.


  1. Macknin ML, Medendorp SV, Maier MC, Infant sleep and bedtime cereal. Am J Dis Child 1989 Sep; 143(9):1066-8
  2. Hall RT, Infant feeding. Pediatr Rev – 2000 Jun; 21(6): 191-9.
  3. Cohen EA, Hadash A, Shehadeh N, Pillar G, Breastfeeding may improve nocturnal sleep and reduce infantile colic: potential role of breast milk melatonin. Eur J Pediatr. 2012 Apr;171(4):729-32.
Published on: February 20, 2017
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Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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Recent Comments

How about right before you go to sleep? Maybe your milk has already changed some at that point?

In a day I breast feed my baby
At night I m unable to do as lack of sleep
So when should I pump milk for baby to have at night

How about right before you go to sleep? Maybe your milk has already changed some at that point?

Wow! There is a ton of great information in this article. I have bookmarked your page so I can come back from time to time. This will surely give the right insight about breastfeeding.

Hi Dr. Greene,

I have a stash of breastmilk in my freezer, but I only pump at night. Will it affect my baby’s nap schedule if I give her night-pumped milk during the day? Or will it just make her drowsy? Do you know if the level of melatonin is significant enough to throw her off her schedule?