Pregnant women who eat more of a key fatty acid found in fish give their babies better chances of mature brain development, finds a new study in the September issue of the American Journal of Clinical Nutrition.

The study also found that mothers with more docosahexaenoic acid (DHA) in their blood had babies with heartier sleep patterns in the first 48 hours after delivery compared to those whose mothers consumed less of the compound.

In a report on the study, Healthscoutnews noted that infant sleep patterns are thought to reflect the maturity of a child's nervous system, and have been associated with more rapid development in their first year of life.

The omega-3 fatty acid, DHA, along with another substance, arachidonic acid (AA), are key building blocks in breast milk that contribute to healthy brain and eye development. Infant formula makers, such as Ross Products and Mead Johnson Nutritionals, are beginning to recognise the value of the compounds and have said they will add them to some of their brands.

The two substances are also passed from mother to foetus across the placenta. Some 70 per cent of brain cell development takes place during gestation.

In the study, Carol Lammi-Keefe and her colleagues at the University of Connecticut compared DHA levels and newborn sleep patterns in 17 women and their babies. Ten of the women had high blood concentrations of DHA - considered to be more than 3 per cent of their total circulating fatty acids - while seven had less than that amount.

Healthscoutnews noted that Lammi-Keefe's group did not ask the women about their diets. None of the subjects in the study had DHA levels that reflected eating fish more than three times a week, as recommended by many experts. Other foods, like eggs and red meat, contain modest amounts of the nutrient, but cold-water fish such as tuna and mackerel are considered the best source.

Women with low DHA were more likely to be minorities and to have received fewer years of education. They were also five years younger, on average, than those in the high DHA category - 24 versus 29 years, according to the report.

All the babies were delivered vaginally, and none of the women had been given drugs known to make newborns lethargic, the researchers said.

Using a motion-sensing pad to measure breathing and movement during sleep cycles, the researchers found babies of women in the low-DHA group had less advanced sleeping patterns than the other infants. They had a greater ratio of "active" to "quiet" sleep, spent more time transitioning between sleeping and waking, and spent less time fully awake than those of women with higher blood levels of the fatty acid.

"As an infant matures, normally you would see the infant spending more time in a wakeful state," Lammi-Keefe said. "Infants born to mothers with more DHA have sleep characteristics of a more mature central nervous system compared with the infants of mothers with lower DHA levels."

June Machover Reinisch, director emerita of the Kinsey Institute and a child development expert, said the findings seemed to echo the importance of breast feeding for optimal infant growth, although she noted that many other factors, from method of delivery and the use of anesthesia during labour to the infant's gender, can influence a newborn's wakefulness.

"We have to be flexible in our definition of development," Machover Reinisch said. "With the child who sleeps not as well at two days, it may be related to the DHA, but it doesn't necessarily mean that there's going to be a problem with that child."

Researchers have correlated newborn sleep states with performance on mental and motor developmental tests at 9 months of age. However, both Lammi-Keefe and Reinisch said there is no way to predict whether a child with less mature sleeping habits in the first week of life will be anything other than healthy.

The researchers are currently organising a one-year study to investigate dietary intake of DHA in pregnant women.