Daily massage can speed up the growth of premature babies who were exposed to cocaine in the womb, a study says. As a result, the babies were able to leave the hospital about four days earlier on average than non-massaged premature infants, researcher Tiffany Field said Monday. Faster-growing babies also become more responsive, which promotes interaction with parents, she said. Other research shows that parental involvement helps a child's development in the first year of life, she said. Fetuses are exposed to cocaine when a pregnant woman uses the drug. Such use raises the risk of premature birth. Field is a professor of pediatrics, psychology and psychiatry at the University of Miami Medical School. She reported preliminary results from the study at the annual meeting of the American Psychological Association, and discussed it in a later interview. The meeting concludes Tuesday. The study, still in progress, has so far produced data on 16 infants. They were born about 10 weeks before their due dates, weighing about 2.6 pounds. They had to stay 20 days to 30 days in a neonatal intensive care unit. Normally, such children then require about 20 days in the hospital simply to gain enough weight to be discharged, Field said. The massage program took place during this latter period. Infants were massaged with firmness, Field said. ``They love it when you give them a little pressure,'' she said. The routine included 10 seconds of working over the top of the head and down to the neck, and then 10 seconds going the other way, she said. Also massaged were the neck and shoulders, back, legs and arms. The chest and abdomen were avoided because the infants obviously did not like being touched there, perhaps associating it with painful medical procedures, Field said. After five minutes of massage, the babies' arms and legs were moved about for five minutes, and then came five more minutes of massage. The 15-minute sessions were done three times a day for 10 days. The massaged babies gained 28 percent more weight per day after the treatment than a comparison group of 16 premature infants who had also been exposed to cocaine, but who were not massaged, Field said. The difference appeared around the sixth day of the treatment and continued for at least a few days after it ended, when researchers stopped keeping track, Field said. Nobody knows why massage spurs growth, but perhaps it stimulates release of hormones that aid absorption of food, she said. Prior studies of premature babies have shown simply holding or paying attention to them did not cause them to gain weight, Field said. The massage treatment looks promising, said a prominent pediatric researcher, Dr. T. Berry Brazelton of Cambridge, Mass. But he cautioned that ``it has to be done with sensitivity to the baby's condition and responses.'' The massager must ease up in response to signals from the infant, he said. Massage had already been shown to speed up the growth of premature infants not exposed to cocaine, Field said. In one study, a 10-day course of daily massage spurred weight gain by 47 percent. The massaged infants were able to leave the hospital six days sooner, saving substantial sums of money in health care costs, Field said. About 10 percent of births in the United States are premature, amounting to 350,000 a year, according to the March of Dimes Birth Defects Foundation. Most premature infants weigh less than 5.5 pounds at birth. About 15 percent to 20 percent of premature infants die in the first month after birth.