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Milk Production Overview


Your milk factory is built in stages. Breast development starts in utero, takes a break, then starts up again during puberty. By the time those stages are finished, you have a basic factory with a “skeleton team” of milk-making cells that are waiting for the message to wake up, multiply and get going, like a winter tree that wakes up and starts growing during spring. Pregnancy (spring) sends the message to start building out the interior of the milk factory and hire more workers. All of these changes inside the breast typically cause tenderness and enlargement, with an average increase of one bra cup or band size.  Your body must also ramp up a transportation system to bring lots of nutrients into the factory to create milk, often noticed as more prominent veining on the surface of the breast. Somewhere around the middle of pregnancy your breasts begin to produce and store colostrum, the first milk that will provide baby with crucial immune factors once he enters the world. Once baby is born, the factory kicks into high gear, like a fruiting tree in summer. And as breastfeeding ends, the factory slows down and assembly lines not needed are dismantled, just as a tree sheds its leave in the fall when it has finished giving fruit.

Seasons of fruit tree original- Taina Li
The Milk Factory


Breast development during both puberty and pregnancy is driven by hormones. Estrogen and progesterone are primary in puberty and continue to play a smaller role during each menstrual cycle thereafter. In pregnancy, estrogen, progesterone, prolactin and human placental lactogen work together with thyroid, insulin and other hormones to “build out” the interior of the milk factory; the placenta drives much of this process. Breasts don’t reach full maturity until the end of your first pregnancy.

Once baby arrives and the placenta comes out, the drop in progesterone triggers a new hormonal cascade that signals the milk factory to start up. Milk production begins to increase around the 2nd to 3rd day after delivery and the composition changes from colostrum to transitional (yellowish) milk that eventually turns a whiter color over the first few weeks.                       



Hormones may start the process, but what is—or isn’t—happening at the breast plays a huge role in building up your milk supply. Frequent removal of colostrum and milk tells the factory to speed up production and make lots of milk. On the flip side, infrequent milk removal leads to  

sluggish milk production. Research shows that the breasts are calibrated to make the most milk when milk is removed frequently and effectively from the start.






















Parents often ask about how often to feed their baby. Most newborns are feeding 10 or more times in 24 hours at the start. Many but not all will gradually slow down to about 8 daily feedings. The reason for this variation is strongly related to the storage capacity of the breast. We aren’t talking about the external size of the breast, but how much storage space there is inside, which varies between women. When storage space is limited, the amount baby can take at one sitting is also limited. However, breasts with smaller storage capacity tend to make and replace milk very quickly because they are drained every time. These babies will always feed more often, closer to every 2 hours. When breast storage is large, a baby can drink as much as his stomach can hold, and he can go longer between feedings, often every 3 hours and occasionally longer still. These breasts make milk more slowly because excess milk is still available.  



Letting your baby call the shots and feed whenever he wants is the best way to make sure he gets enough milk. Our job is to pay attention to what our baby is saying and follow his lead. If you’re a left-brained, give-me-the-instruction-book-please kind of person, this can be difficult at first. But Nature made lactation to be a right-brained process, with the mother/parent responding to baby’s cues rather than a clock. The only exception we make to nature’s rule is if the baby is not feeding often enough due to prematurity, jaundice, or other issues. In those cases, a baby may need to be prodded to feed more often until their issues improve.  



Your body is always making milk; faster when the warehouse is emptier, and slower when it’s full. The milk is held back until a request for delivery is presented. Oxytocin is then released by the pituitary and flows to the breast through your blood stream, where it triggers muscles in the storage area to contract and push some of the milk down towards baby. This flow lasts a few minutes then slows down; if baby continues to suck hungrily, another delivery will be triggered again to provide more milk. You can have multiple letdowns in a feeding; how often varies with each individual and also on the signals baby sends.  When the breast is pushing and the baby is pulling, milk flows easily. When the breast stops pushing, it is harder for a baby to get milk out until the next delivery, which is why babies will feed fast then slow then fast again. The letdown reflex may work inconsistently in the beginning but usually becomes quite automatic overtime. While sucking stimulation is a major trigger of this reflex, emotions can also affect it;  just thinking it is feeding time and/or hearing baby stir or cry can cause a letdown, while high stress or anticipation of pain can temporarily inhibit the reflex (and frustrate a hungry baby!).  Important tip: just because milk isn’t coming out easily right now doesn’t mean you’ve run out!   

Boss 2018- f1000research-7-15731-g0000[1
How Your Body Knows
Storage Capacity
Baby Calls the Shots

Boss, M., Gardner, H., & Hartmann, P. (2018). Normal Human Lactation: closing the gap. F1000Research, 7((F1000 Faculty Rev)), 801. doi:10.12688/f1000research.14452.1

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