Fatima Gonzalez, a lactation consultant at Miami Children’s, still encourages breastfeeding as the healthiest option for both the mother and baby, but since 2008 she has been able to offer her patients donated human milk instead of formula if necessary.

“A lot of families don’t realize that formula is derived from cow’s milk, which is not easily digested,” Gonzalez said. “It’s imperative that it is from the same species, because the immunological properties that the breast milk has, there’s no formula that can replicate.”

At Joe DiMaggio Children’s Hospital in Hollywood, lactation consultant Marianne Cesarotti said 80 percent of premature babies get some donor breast milk, even if only for the first few feeding sessions.

“It can take mom three to four days to start producing milk,” she said of mothers who give birth prematurely. “If there’s any delay, we need to use donor milk as that initial bridge until mom’s milk is available.”

Only 5 percent of babies at Joe DiMaggio continue receiving donor milk, Cesarotti said, in the rare cases of “lactation failure.”

Although many studies have proven the beneficial properties of human breast milk, the specifics are still not fully understood. A Duke University study published last month found that human breast milk promotes “normal” growth of bacteria found in the digestive tracts of infants. William Parker, the study’s author, said without these bacteria, immune system development could get “thrown off track.”

“You can put bacteria in a test tube of breast milk and they start growing [normally] in clumps and films. Put that bacteria in a test tube of infant formula and they grow randomly,” Parker said. “A middle schooler could do this experiment and see that this is the case, but we’re still not exactly sure why breast milk has this effect.”

Parker said his next experiment will be to test bacteria growth in pasteurized breast milk to see if it behaves more like raw breast milk or formula.

All human breast milk at HMBANA banks is pasteurized, a flash-heating process that kills harmful pathogens that could be deadly for a fragile infant. In pasteurization, some of the beneficial bacteria are killed as well, which is one reason why a mother’s own milk is always the first option for newborns.

There are some informal breast milk exchanges organized locally or in online forums, but Jean Drulis of HMBANA and other health professionals caution against “casual sharing of milk” that is not screened for diseases like HIV and hepatitis.

Carral gave her first donation while she was still at Texas Children’s Hospital and sent additional donations over the next few months from her Coral Gables home. She is looking into training programs to become a certified lactation consultant because she wants to help mothers who have trouble breastfeeding.

“When my daughter was in the hospital it was really a terrible time for me, but I feel lucky because I had a happy ending,” Carral said. “I hope my donation helped other mothers have a happy ending, too.”