"These results expand our understanding of the influence of sleep position on motor skills," says lead study author Carl E. Hunt, M.D., director of the National Center for Sleep Disorders Research at the National Heart, Lung and Blood Institute.

These results do not in any way suggest that babies should be placed on their fronts to sleep, says Hunt and colleagues in the study published in the October issue of the Journal of Developmental and Behavioral Pediatrics.

With evidence growing in the 1990s that face down sleeping increases the risk of SIDS, the American Academy of Pediatrics advised parents to put infants to sleep on their backs or sides. This public awareness campaign resulted in a 41% decrease in SIDS deaths between 1990 and 1997.

Hunt, who conducted this study while at Medical College of Ohio, analyzed data on more than 200 prematurely born infants enrolled in the Collaborative Home Infant Monitoring Evaluation (CHIME), a long-term study of premature infants' physical and mental capabilities.

While infants who slept on their stomachs, backs or sides had similar overall scores on a test of motor skills development, scores varied on specific aspects of the test. Back sleepers were less likely than stomach sleepers to be able to raise their head by 45 degrees and lower it with control at 56 weeks of age. And side and back sleepers were less likely than stomach sleepers to be able to raise their head by 90 degrees and lower it with control.

There were no differences between stomach, back and side sleepers in terms of mental development, the researchers found. These findings for premature infants need to be confirmed with full-term infants, Hunt says.

Infants usually placed to sleep on their stomachs, rather than on their sides or backs, may have more opportunities to develop strong neck muscles and improve head control-but these finding don't suggest parents should put infants to sleep face down.

Instead, parents can give infants who sleep on their backs opportunities to develop strong neck muscles. The researchers suggest that, under parental supervision, these infants can play on their stomachs during the day.

This study was supported with funding from National Institute of Child Health and Human Development.

The Journal of Developmental and Behavioral Pediatrics is published bimonthly by the Society for Developmental and Behavioral Pediatrics. For information about the journal, contact Mary Sharkey at (212) 595-7717.