When both of her sons were born prematurely, Keely Shaw wanted to feed them breast milk to bulk them up.

But because her body wasn't yet making enough milk, Shaw, of Arvada, Colo., turned to a nationwide system that collects donated milk from nursing mothers and distributes it to babies in need.

Shaw's two boys received milk donated through the Mothers' Milk Bank at Presbyterian/St. Luke's Medical Center in Denver until she could provide enough of her own, she says.

"I think it must be similar to what people who receive donated blood must feel," Shaw says. "This kind of gift is so personal and can be monumental for those who receive it."

With a growing number of doctors saying breast milk is the best food for babies, especially hospitalized preemies struggling to gain weight, the demand for milk donations is increasing. The amount of donated milk distributed by the 10 banks of the Human Milk Banking Association of North America is growing rapidly but is still far below what's needed, says Pauline Sakamoto, president of the association.

Milk bank managers say federal, state and local health authorities are more aggressively promoting breast milk than in the past, prompting the demand from mothers who can't provide enough for their own children.

Movement is growing

About 2,000 women donated breast milk through the banks in 2008, Sakamoto says, and many more helped their friends through informal arrangements. Three new milk banks are forming in Kansas City, Newton, Mass., and Portland, Ore., she says. Hospitals pay a handling fee of $3 to $5 an ounce for the donated milk collected by the milk banks, which they test, pasteurize and freeze until it's needed.

Milk banks have simply formalized a system that has been around for thousands of years, says Bettina Forbes, director of the advocacy foundation Best for Babes, which helps mothers fight the societal "booby traps" they face if they choose to breast-feed.

"There's sort of a 'yuck factor' with breast-feeding and breast milk," she says. "But it's like donated blood."

Mandy Belfort, a neonatologist at Children's Hospital Boston, says some women don't produce enough milk, often because their babies are born early.

Actress Alysia Reiner, who gave birth to a daughter, Livia, in December 2008, tells of a close friend whose daughter was born about six months later. Her friend struggled to produce enough milk, so the two agreed to share. "I had a freezer full of liquid gold and didn't want it to go to waste," says Reiner, who has appeared in the movie Sidewaysand in various television shows.

Donating milk "is simply an area so many women don't know about," she says. "They say 'What, a milk bank? No way.' "

Breast milk is better for baby

Sakamoto says that although most babies can feed on either formula or breast milk, physicians say breast milk is generally best.

"There's also some evidence that preterm babies who receive breast milk have better developmental outcomes than babies that receive formula," Belfort says. "In New England, we are starting to talk more and more about using donor milk more routinely."

La Leche League International, which advocates breast-feeding, believes donated breast milk provides an important option for women who can't breast-feed, says spokeswoman Loretta McCallister. "Breast milk will help the baby get up to the good birth weight. It has antibodies that help fight infections and helps them develop."

A 3-month-old baby can consume up to a quart of milk a day, says Laraine Lockhart Borman, manager of Mothers' Milk Bank at Presbyterian/St. Luke's in Denver. Most women produce more than enough, she says. "Some mothers produce enough for triplets or quadruplets."

Milk donors must be healthy

Borman notes the milk bank usually has about 100 mothers donating but saw the number drop to about 50 at the turn of the year. That created a shortage of milk, in part because of seasonal flu vaccinations. Women must be healthy to donate through the milk banks, which require a three-month wait after a woman gets the flu vaccine before she can resume donations. Borman says any mother who can give blood is eligible to donate breast milk.

Donor mothers use a vacuum pump to extract and bottle the milk. Says Shaw: "Pumping to donate is the very least I can do to repay what was done for us."