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Can You Pump Into The Same Bottle All Day? The Answer, According To A Lactation Consultant

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When you're making the choice to breastfeed (either exclusively or combined with formula-feeding), every drop of milk you produce is precious. Particularly for moms who pump between feedings or at work, it's important to know how to care for expressed milk. For example, can you pump into the same bottle all day? Or do you have to use separate bottles each time you pump? After spending so much time squeezing a manual pump or being attached to an electric one, you do not want to have to toss the whole batch because it's not safe to feed to your baby.

Thankfully, nursing moms don't have to keep a dozen bottles handy every time they want to make a take-out meal for their baby. As New York-based certified lactation consultant Jane Weiser, Ed.D., RN, IBCLC, RLC, explains to Romper, it's safe to add new expressed milk to an existing batch — as long as you know how to do it correctly. "I provide patients with evidence-based information on collection, storage, and handling of breast milk," she says. She stands by the recommendations of the Centers for Disease Control (CDC) and the Academy of Breastfeeding Medicine (ABM).

It can be discouraging to pump just an ounce or two of milk at a time, but it's actually not an unusual situation, particularly for mothers who use manual pumps rather than electric ones. So it seems only logical to combine the milk from several pumping sessions to make one or two larger portions for baby's next feed.

The main issue here is the temperature of the milk. Freshly expressed breast milk can be left at room temperature for up to 4 hours, according to the ABM and CDC. So if you plan to pump twice within that time period, you can store the bottle on the countertop between sessions and pump into it again. Then feed it directly to the baby, or refrigerate or freeze it for a later feeding.

Things get more complicated if you put your bottle into the fridge after the first pumping. The ABM warned against adding newly pumped breast milk to previously chilled milk; this warms up the cold milk and invites the growth of bacteria. To combine the portions, you'll need to pump into a new bottle, then refrigerate it and mix it with the older milk when it's cold enough. Refrigerated milk can be safely used within a 4-day period; depending on your baby's preferences, you can feed directly from the fridge, or warm it up in lukewarm (not hot) water.

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Same goes for milk that you've already stored in the freezer after pumping. If you want to add fresh milk to a frozen batch, the safest approach is to thaw the frozen milk by refrigerating it or putting it in a warm-water bath, then pouring in the new milk once the frozen milk is at room temperature. Again, you'll need to pump the fresh milk into a new bottle, so you can't use the frozen milk bag or container for another pumping session. The CDC guidelines cautioned that moms should never refreeze breast milk that has already been thawed.

If your baby doesn't finish a bottle of breast milk — whether it's a totally fresh batch, or a mixture of milk from separate pumping sessions — it's okay to serve the leftover milk again within two hours after the last feed. But if it's been more than two hours, dump it; the risk of contamination from the baby's mouth and the milk itself isn't worth it, per the ABM.

No matter how you choose to pump, store, and feed, it's important to make sure your pump and accessories are cleaned between uses. The CDC recommended washing pump parts in "a clean basin with soap and water" rather than in a sink, which could invite contamination. Sanitizing the feeding items with boiling water, in the microwave, or in the dishwasher will also ensure the pump is clean between uses.