There are several reasons a baby may not remain with the birth parent including adoption, foster care, parent illness or incapacity or incarceration. In the most difficult circumstances, a baby may have died.
Your body will still make milk to feed the absent child. Some parents choose to donate their breast milk in the following ways:
Donate to a Milk Bank
Various non-profit organizations accept expressed breast milk. The donations are screened and pasteurized and then used for vulnerable or fragile babies who are not able to receive their own mothers' milk.
Other parents may stop their milk supply as quickly as possible. Do this in a safe and healthy way to avoid complications such as infection.