To manage your milk supply, it helps to know the mechanics, so here’s a primer on milk production:
However much milk is removed (either via baby or pump), the body produces a replacement quantity, so the more milk removed, the more replacement milk produced. If you pump longer than the milk is flowing, you will be giving your body the message to produce more than your current supply, so if you’re concerned about your supply, pump a little longer after the flow slows down. To this end, if you pump for another 5 minutes or so, you will often have another letdown and milk flow will begin again.
Some women find they can increase production by pumping until the milk flow slows down, then stop and massage breasts for a few minutes and then start pumping again. You may get more milk that way than by simply leaving the pump on.
So what exactly is a milk letdown? It is the milk ejection reflex that causes muscle contractions (which are not painful) around the milk ducts and other surrounding muscles to squeeze milk through the ducts towards the nipple. You may feel it as a “tightening” of your breasts, a tingling in your areolas or a mild ache, or you may not feel it at all. In reality, your baby isn’t sucking milk out of the ducts; but only the milk that has been pushed to the nipple by the letdown. When you massage your breasts to trigger more production, as suggested above, you are recreating what the letdown does by moving milk along your ducts to the nipple.
And how does the letdown happen? It is caused by the hormone oxytocin, which is produced when your baby is suckling at your breast, but oxytocin production soon becomes a conditioned response so that you may experience a letdown simply by thinking about your baby nursing, or about the letdown itself. By the way, breasts have a long memory: You will experience letdowns long after your baby stops nursing. On the other hand, stress and pain interfere with the ability to have letdowns because they interfere with oxytocin release.
Not surprisingly, the brain, (pituitary gland specifically) is responsible for oxytocin release, and here’s a story to highlight this: A mother who had premature twins couldn’t breastfeed for weeks, so she was pumping to maintain supply. When the babies came home, and she put them to the breast, she couldn’t have a letdown, even though she had had no problem with letdowns when pumping. She was producing the milk, but it couldn’t get to her nipples.
The lactation consultant she worked with figured out that her brain had been trained to think of the pump as her babies, and so it didn’t know what to do when the actual babies were doing the sucking! The solution was to run the pump while she was nursing the babies to trigger letdown until the brain was “retrained”.
The takeaway: If you have trouble with letdowns when pumping, bring a picture of your baby or something that smells like your baby to trigger your brain into oxytocin release.
And here’s an interesting fact: Milk production is temporal - you may produce more milk on Mondays than on Fridays because you just spent the weekend breastfeeding. And here’s a myth buster: You do not have to drink milk to make milk. (How many cows drink milk?) Drinking liquids will not increase your milk supply. Milk is made from blood and stored body fat. But this doesn't mean you shouldn't hydrate - stay hydrated for other reasons!