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

Breast pump and young mother. Night vs day milk.Learning to breastfeed your baby can be one of the most challenging and beautiful experiences of being a new parent. Many moms choose to also learn how to pump their breastmilk for times when they can’t be there to nourish their little one, or for other reasons. Here are some new insights I’ve learned and answers to questions that often come up around pumping.

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 breast feeding 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.

Note: Dr. Greene is an Advisor to Naya Health, makers of the hospital-grade breast pump pictured above. It is design to provide a high quality, quiet, comfortable pumping experience.


  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.

Dr. Alan Greene

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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  1. Neha

    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

    • Lenni Doyel

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

  2. Emma Gedge

    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.

  3. Tiffany

    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?


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