Putting babies to sleep on their back has contributed to a dramatic drop in the rate of Sudden Infant Death Syndrome (SIDS).

A new study, though, shows that this decline has plateaued in recent years. Researchers also point out that several factors beyond an infant’s sleep environment has played a role in the decrease..

According to the new study, published today in the journal Pediatrics, the number of deaths attributed to SIDS went down 71 percent between 1983 and 2012.

However, SIDS remains the leading cause of death among babies between 1 month and 1 year of age. In 2010, more than 2,000 infants died of SIDS.

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Campaign Changes Sleeping Habits

Much of the decline in SIDS deaths occurred after the start of the Back to Sleep campaign —now known as Safe to Sleep.

This campaign started in 1992. It stemmed from recommendations made by the American Academy of Pediatrics that parents avoid putting babies to sleep on their stomachs and make sure their crib was free of items that could suffocate them.

The number of parents placing their infants in the face-down position for sleep decreased from 70 percent in 1992 to 24 percent in 1996.

During those four years, the rate of SIDS deaths in the United States fell by 38 percent.

"It is true without any qualification that it is safest for babies to sleep on their backs,” said study author Dr. Richard Goldstein, a pediatrician in the Pediatric Advanced Care Team at Boston Children's Hospital and Dana-Farber Cancer Institute, in a press release. “This study and others have shown it.”

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Not Every Crib Death is SIDS

The authors of the study and others caution that the drop in SIDS deaths may not be as dramatic as it appears.

“We can’t really say that we’ve reduced it 71 percent,” said Dr. Cristina Miller, a neonatologist with Children's Hospitals and Clinics of Minnesota, in an interview with Healthline. “We’ve probably reduced it around 30 to 40 percent by Back-to-Sleep and changes in the environmental factors.”

One reason for this is that over the past decade there has been a shift in how medical examiners and investigators classify infant deaths. Some deaths that would have once been recorded as SIDS are now “cause unknown” or “accidental suffocation or strangulation in bed.”

“When we’ve seen the SIDS go down, we’ve seen infant deaths from asphyxiation, loose bedding and things like that go up,” said Miller.

This recoding of deaths may also partially explain the recent plateau in SIDS numbers.

The rate of overall sudden unexpected infant death has been falling over the past 30 years. This broad category includes SIDS as well as known causes of death such as suffocation or infection.

"The decline in SIDS deaths follows decreases in infant deaths from known causes," said Goldstein. "This suggests that broad trends in the health of pregnant women and babies influence infant mortality across the board.”

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Infants Face SIDS Triple Threat

When it comes to SIDS, infants face what Miller calls a “triple threat.”

First, infants are most at risk for SIDS between 1 and 4 months. This, coupled with the environmental factors, increases their risk during the early months of their life.

Because of that, an emphasis has been placed on educating parents about creating the healthiest environment for their babies. This has paid off.

In addition, a large part of the overall drop in infant deaths “has to do with big initiatives in maternal smoking,” said Miller. “Maternal smoking has decreased dramatically since the ’70s.”

The researchers say that smoking by pregnant women decreased from 16 percent in 1987 to 10 percent in 2011. Improved steroid medications for treating infants with respiratory distress syndrome — often seen in premature babies — has also decreased the number of deaths.

Other factors that have played a role in reducing SIDS include increased access to prenatal care and increased breastfeeding.

“Although environmental risk factors for SIDS are very important — and it’s really important that we continue to educate families and parents about those risk factors — it’s not the whole story,” said Miller.

The third part of the story has to do with the underlying biology of SIDS, which affects each infant differently.

“Some babies are just more at risk for some intrinsic reason,” said Miller. “Now that we’ve worked on that external, environmental piece, we’ve still got work to do in that intrinsic piece.”