Researchers examined survey data from a nationally representative sample of U.S. mothers. More than three in four mothers said they usually placed their infants on their backs to sleep, the survey found.

But just 44% of the mothers said they planned to place babies to sleep on their backs and then actually did this every time, researchers report in Pediatrics, online August 21.

“Intention does not always match practice,” said lead study author Dr. Eve Colson of the Yale School of Medicine in New Haven, Connecticut.

“While families may intend to place infants on the back to sleep and may eventually do so, they do not always follow these recommendations,” Colson said by email.

In 1992, the American Academy of Pediatrics (AAP) announced that babies should be placed on their backs to sleep, in order to lower their risk for Sudden Infant Death Syndrome (SIDS).

Despite a dramatic decrease in frequency, SIDS still remains a leading cause of infant mortality. Nationwide, SIDS kills about four babies out of every 10,000 live births, down from about 130 in 10,000 in 1990, according to the Centers for Disease Control and Prevention.

To prevent SIDS, along with putting young infants to sleep on their backs, the AAP also encourages breastfeeding, pacifier use and firm crib mattresses while advising against blankets, pillows and bed sharing.

For the new study, researchers examined survey data collected from 3,297 mothers of infants from 2 to 6 months old.

Overall, 77% of the women said they usually put babies to sleep on their backs, while about 14% said they typically put babies to sleep on their sides and roughly 8% routinely put babies down on their stomachs.

Mothers who were African-American or didn’t complete high school were more likely to put babies to sleep on their stomachs.

While 58% of the mothers said they intended to put infants down on their backs all the time, only 44% said they followed through each time their baby went to sleep.

When doctors explained safe sleep practices, women were 40% less likely to report putting babies to sleep on their stomachs, and 50% less likely to put infants to sleep on their sides, the study also found.

The study wasn’t a controlled experiment designed to show whether or how educating women about infant sleep safety might influence how babies actually went to sleep or their odds of dying during the night.

It also doesn’t explain why some parents didn’t always put babies to sleep on their backs, said Michael Gradisar, a psychology researcher at Flinders University in Adelaide, Australia, who wasn’t involved in the study.

“If we can get parents to explain their decision in their own words, then we can begin to understand what factors are more important in their decision making than following recommended safe sleeping practices,” Gradisar said by email.

Still, the results underscore a need for better education, said Dr. Michael Goodstein, a neonatologist for WellSpan York Hospital and a member of the AAP Task Force on SIDS.

“We still have a lot of work to do, and lives are at stake,” Goodstein, author of an accompanying editorial, said by email.

“If we can’t find ways to work with families to achieve behavior change, so that parents want to keep their babies supine and believe that it makes a difference, then we are not going to see further gains in terms of reducing sleep-related deaths and our postnatal infant mortality rate in the U.S.,” Goodstein added.