The nutrients and calories in human milk are often enough for "older" or "bigger" premature babies, and for many other high-risk babies. But lower nutrient levels and the "full-term" calorie count in human milk may cause problems for a low-birth-weight baby who weighed 3 pounds, 5 ounces (1,500 grams) or less at birth. Very preterm and low-birth-weight babies miss the growth of fat, muscle, and bones that usually happens in the last few weeks of pregnancy. To "catch up" on this growth, they need a boost of protein and minerals that breastmilk alone can't provide. They also may need more calories.
Fortunately, adding to (fortifying) your milk won't lessen the nutritional and anti-infective benefits your baby will gain from getting your milk. But it may help to better provide the nutrition your baby needs.
The most common ways of adding nutrients and calories are:
Hindmilk feeding. When a higher calorie count is the only concern, you may be asked to pump your milk for several minutes and then stop to change collection bottles to collect the rest of the milk. The early milk you get while pumping is called foremilk. It's valuable and has many nutrients and protective factors, but it is lower in fat and calories than the milk you pump later. This milk collected after the first several minutes is called hindmilk. This tends to be higher in calorie-rich fats. Freeze any foremilk for later use. Only use this strategy if told to do so by your baby's healthcare provider.
Human milk fortifier (HMF). HMF adds to the nutrients already in your breastmilk to meet your baby's higher requirements. It supplies increased protein for growth and minerals calcium and phosphorous that low birth weight and some high-risk babies need for correct bone development. HMF is added directly to a bottle of your own milk. Often a powdered version is used when you have plenty of your own milk. Liquid HMF will be used if you have reduced amounts of your breastmilk.
Premature infant formulas. Sometimes feedings of mother's milk may be alternated with feedings of a premature infant formula. This may be done if HMF is not thought to be the best choice, or when you have reduced amounts of your breastmilk.
How long your baby needs added nutrients and calories will depend on your baby's age, weight, health, and how well they can breastfeed.