Breast milk refers to the milk produced by a mother to feed her baby. It provides the primary source of nutrition for newborns before they are able to eat and digest other foods; older infants and toddlers may continue to be breastfed.
The baby nursing from its own mother is the most ordinary way of obtaining breastmilk, but the milk can be pumped and then fed by baby bottle, cup and/or spoon, supplementation drip system, and nasogastric tube. Breastmilk can be supplied by a woman other than the baby's mother; this is known as wetnursing.
Under the influence of the hormones prolactin and oxytocin, women produce milk after childbirth to feed the baby. The initial milk produced is often referred to as colostrum, which is high in the immunoglobulin IgA, which coats the gastrointestinal tract. This helps to protect the newborn until its own immune system is functioning properly along with creating a mild laxative effect, expelling meconium and helping to prevent the build up of bilirubin (a contributory factor in jaundice).
There are many reasons a mother may not produce enough breast milk. Some of the most common are: improper latch, not nursing or pumping enough to meet supply, certain medications, birth control, illness, dehydration, or, rarely a physical inability to produce which could be caused by prolactin deficiency due to Sheehan's syndrome or hypopituitarism when there is a sudden drop in blood pressure during child birth. This rare syndrome may require hormone replacements.
Lack of supply can be addressed by nursing or/and pumping more frequently. The more the mother nurses her baby, or pumps, the more milk is produced.
It is very helpful to nurse on demand - to nurse when the baby wants to nurse rather than on a schedule. If pumping; it is helpful to have an electric high grade pump so that all of the milk ducts are stimulated. Some mothers try to increase their milk supply in other ways - by taking the herb fenugreek, used for hundreds of years to increase supply ("Mother's Milk" teas contain fenugreek as well as other supply-increasing herbs); there are also prescription medications that can be used, such as Domperidone (off-label use) and Reglan.Increasers of milk supply are known as galactagogues.
Source: wikipedia
