Breast Milk Associated With Greater Mental Development In Preterm Infants
Extremely low birth weight premature infants who received breast milk shortly after birth, while still in intensive care units, had greater mental development scores at 30 months than did infants who were not fed breast milk, reported researchers in an NIH network. Moreover, infants fed breast milk were less likely to have been re-hospitalized after their initial discharge than were the infants not fed breast milk.
The study is a follow up to a previous study in which the same infants were tested at 18 months, showing that the breast-fed infants held the developmental gains seen in the earlier study.
"These findings strongly suggest that, whenever possible, preterm infants should routinely be given breast milk during their stay in the intensive care unit," said Duane Alexander, M.D., Director of the NICHD, the NIH institute that conducted the study.
The study appears in the October 1 issue of Pediatrics. Betty R. Vohr, M.D., of the Department of Pediatrics at Brown Medical School, led a team of researchers in the NICHD Neonatal Research Network, at her own and other institutions, to conduct the study.
Extremely low birth weight infants are the tiniest and most fragile of premature infants, weighing less than 1,000 grams, or 2.2 pounds, at birth, explained Rose Higgins, M.D., the NICHD author of the current study and the program officer for the NICHD Neonatal Research Network. This category of infants makes up about 1 percent of all U.S. births, or roughly 40,000 each year.
Researchers have long known the benefits of breast milk for full term infants, but its potential effects in preterm infants had not been well studied, Dr. Higgins added. Full term infants given breast milk are less likely to develop diarrheal diseases, skin allergies, ear infections, or upper respiratory infections. Some studies indicate that they are less likely to be overweight or obese as adults. To conduct the study, the researchers tracked the breast milk intake of 773 extremely low birth weight infants in the neonatal intensive care units at 12 sites in the NICHD Neonatal Research Network, between 1999 and 2001.
The children in the current study were divided into five groups by the quantity of breast milk they had ingested while in the NICU. The majority of the infants had been given at least some breast milk while in the NICU. Only about one-fifth of the children in the study had not been fed any breast milk.
The researchers found that the benefits of breast milk first seen at 18 months were still present at 30 months. Children who had been given breast milk received higher scores on the Mental Developmental Index (MDI), a test measuring the children's overall intelligence. The average MDI score was 76.5 for children who had not received any milk in the NICU, compared to a score of 89.7 for children who had received the greatest amount of breast milk. Children who had been given breast milk also showed greater ability to control and appropriately respond to emotions and were also less likely to have been readmitted to the hospital after their discharge and before 30 months.
There was no difference in the amount of growth or the rate of cerebral palsy in children who had received breast milk in the NICU compared with those who had not.
The researchers hypothesized that breast milk may boost the children's immunity against respiratory infections, the principal reason children who had not received breast milk were hospitalized.
"Breast milk offers immune advantages for the infant. It has natural substances that protect against infection," said Dr. Higgins.
Because they are unable to feed themselves, premature infants receive fluids and nutrients intravenously. Gradually, breast milk is dripped into their stomachs through a feeding tube. When the infants are healthy enough, the intravenous tube can be removed and the baby can receive all its nutrition from the feeding tube. In the previous study, the researchers found that infants who had ingested breast milk were able to leave the neonatal intensive care unit sooner and were able to make the transition faster from intravenous feeding to receiving all their nutrition through a feeding tube than were infants receiving formula.
Dr. Higgins explained that earlier studies of term infants had found that infants who were breastfed tended to score higher on tests of mental development than did those who were not. She noted that mothers who breast feed their infants tend to have more education than those who do not breast feed. For this reason, the researchers were unsure whether the breast fed infants' higher test scores resulted from their consumption of breast milk or from the fact that their more educated mothers were able to provide them with greater intellectual stimulation.
In the current study, mothers who provided breast milk for their infants also tended to have more education than those who did not. However, in their analysis of the data, the researchers mathematically compensated for the mothers' educational levels. With this adjustment, the researchers concluded that consumption of breast milk had a positive effect on infants' mental development scales, independent of mothers' educational levels.