The milk let-down, or milk-ejection reflex (abbreviated MER), is when a nursing mother’s milk is being actively released from the cells that produce and store the milk. These cells are called alveoli, and when they constrict and release the milk to flow into the ducts that will deliver milk to the nipple, milk let-down is said to have occurred.
Many women can sense when their milk is letting down. They may feel a tingling sensation in the breast or see milk leaking from the opposite breast. However, not all women sense a let-down, and it is important to know that that can be normal, too! Not having this sensation is not a reason to automatically assume that you aren’t producing milk or that you have an issue with low milk supply.
For women who don’t sense a let-down, there are a few things you can look for to make sure your baby is, in fact, getting milk. A change in suckling patterns — from quick short sucks to long, slower ones where swallowing is heard — is a great indicator that your let-down has happened. Seeing milk at the corner of your baby’s mouth is another giveaway, as is the sound of gulping as your baby happily feeds. Many women also report a feeling of relaxation once their let-down has occurred, so you may notice that too.
Right after delivery, an increase in uterine cramping (and sometimes bleeding) often happens at the same time as the milk let-down. This is all related to hormones. When a baby suckles, this triggers the release of two hormones in a mother: prolactin and oxytocin. The prolactin tells her body to produce milk, while the oxytocin causes the let-down and makes those alveoli start to contract and deliver the milk they’ve stored. It’s also that oxytocin that is responsible for the uterine cramping (which is a good thing — it gets your uterus back to its pre-pregnancy size and thus decreases your bleeding) as well as that feeling of euphoria that so many nursing moms have.
It’s possible to have multiple let-downs during a feed, so you may notice this sensation more than once. It can happen with pumping too, and it is especially easy with pumping to see how significantly the milk flow changes from before (when it’s slower) to after (now much faster) the let-down. Keep in mind pumping is not a perfect replacement for a baby, so if you sense a let-down with your baby but not with the pump, it isn\’t abnormal! As long as you are pumping enough milk to meet your needs, the sensation of a let-down does not matter.
- Riordan and K
- Breastfeeding and Human Lactation, 4th edition.
La Leche League International
- The Breastfeeding Answer Book, 3rd revised edition.
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