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Change in Infant Sleeping Practice Leads to Changes in Motor Developmental Milestones

By Elaine Cassel

Marymount University and Lord Fairfax Community College

Nurture may be changing nature's developmental milestones. The practice of putting infants to sleep on their backs to minimize the risk of Sudden Infant Death Syndrome (SIDS) may be altering what were once considered normal motor developmental milestones.

Parents, and students of developmental psychology, have long measured a baby's progress by certain milestones of motor development. Charts in psychology books, pediatricians' offices, and parents' magazines often depict an infant lifting its head at one month, pushing its chest up with its arms at two and a half months, and rolling over from its stomach to its back at three and a half months. Crawling, though not depicted in many charts because of variations in the timing of its appearance, was generally expected to occur between seven and nine months of age. Walking was thought to be a natural progression from crawling.

But changes in infant sleeping practices may produce changes in the timing and nature of some of these behaviors. In recent years, parents have been encouraged to put babies on their backs to sleep rather than their stomachs; this practice has been associated with a marked reduction in SIDS deaths. Two studies have found that since infants have been increasingly placed on their backs, babies are not lifting their heads, turning over, and crawling according to what we had grown to expect as "normal" timing for motor milestones. Indeed, increasing numbers of babies are not crawling at all but going from sitting up, to pulling up, to walking. It all makes perfect sense, of course. A baby on its back in the crib or playpen has no real incentive to turn over on its stomach in order to see mom or the surroundings, and crawling is simply a natural progression from squirming around on the stomach.

According to a longitudinal study that is following 15,000 British infants from birth in 1990 (the beginning of that country's campaign to encourage back sleeping), fewer babies are lifting their heads, turning over, or crawling when expected. A U.S. study showed similar results. The babies who slept on their backs either started crawling later than expected or not at all.

There appear to be no adverse medical consequences from the changes in motor behaviors. The back-sleepers are starting to walk at the same age as the stomach-sleepers and crawlers--at about one year. Many pediatricians are even telling parents not to look for these milestones anymore. However, they are urging parents to give their wee ones some "stomach" time daily, as it has a soothing effect on the infants--and their caregivers. Putting a baby on its stomach either in a lap or on a shoulder is a time-tested method for getting baby to sleep--especially with the aid of a rocking chair--and giving parents some much-needed quiet. But experts are certain that even though we may have to walk before we run, we don't have to crawl before we walk.


Kolata, G. & Markel, H. (2001, April 29). Baby Not Crawling? Reason Seems to Be Less Tummy Time. The New York Times. Online at

Study: Back Sleeping Best For Babies Despite Potential For Developmental Delays. (1998, November 3). CNN Interactive. Online at

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