Did your breasts become fuller and more tender during pregnancy? This is a sign that your body was hard at work beginning the milk making process. Breast changes during pregnancy are a result of hormones that cause the milk ducts and glandular tissue (milk making cells) to grow and increase in size. The developing placenta stimulates the release of estrogen and progesterone, which increase the size and number of milk ducts in your breasts. Another sign that your breasts are getting ready to produce breast milk is when the little bumps around your areola get bigger and more noticeable. These bumps are called Montgomery glands and are responsible secreting an oil that helps lubricate your nipples.
The hormone oxytocin also rises when your baby suckles. Again, messages from your nipple and breast travel to the pituitary gland and cause the release of oxytocin into the bloodstream. Oxytocin causes the small muscles around your milk making cells to contract and move the milk through the milk ducts. This moving of the milk is called the “let-down reflex”, which can cause a tingling or prickling sensation in your breasts. Your milk may even drip or spray out during a let-down. 
During your second trimester of pregnancy, your breasts start to make colostrum, the thick early milk that is high in antibodies and protein. Once your baby is born and the placenta is delivered, estrogen and progesterone levels drop dramatically and give rise to prolactin and oxytocin. Most mothers report that their mature milk comes in 2-3 days after birth.
Prolactin helps your breasts make milk. Every time your baby breastfeeds, your prolactin levels rise. As your baby suckles, messages from your breast and nipple travel through the nervous system to the pituitary gland in the brain. The pituitary releases prolactin which travels back to the breast through the bloodstream. With each release of prolactin, your body makes more milk in the milk making cells. If the levels of prolactin get too low, your milk supply can decrease.
In order to maintain a good milk supply, it’s important to remove your milk often. If you stretch out your feedings and allow your breasts to get engorged, it signals to your body that you do not need to produce as much milk. This is often a cause to low milk supply. So, for a mother who wishes to maintain her milk supply or increase her milk supply, keeping the breasts as empty as possible throughout the day is ideal.
If you are experiencing a true low milk supply, it is always best to work with an IBCLC to identify the cause.
