New guidelines aimed at reducing the risk of sudden infant death syndrome were released by the American Academy of Pediatrics on Monday and include for the first time a recommendation that babies sleep in the same room as parents — but not the same bed.

For decades, SIDS has bewildered doctors who have studied it and devastated parents who have experienced it: an otherwise healthy infant found dead in his or her crib. The condition is defined as the inexplicable sudden death of a baby younger than 1 year old.

Now, doctors say that allowing a baby to share a room can cut the SIDS risk by as much as 50 percent, which is why the academy is making it official policy.

Past recommendations stipulated that babies sleep only on their backs, never their stomachs or sides. Back sleeping is still strongly recommended, academy officials say.

The new room-sharing guideline — part of a broader policy on SIDS — calls for infants to sleep in a crib or bassinet with a firm mattress in their parents’ bedroom for at least the first six months and, optimally, for the first year of life. Infant sleep-environment measures are part of the academy’s overall policies presented Monday at the annual meeting of the American Academy of Pediatrics in San Francisco.

Room-sharing is based on scientific research that has emerged since 2011, the last time academy guidelines were published on SIDS prevention.

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“We are not recommending the same bed, but the same room,” said Dr. Hank Bernstein, professor of pediatrics at Hofstra-Northwell School of Medicine and a member of the American Academy of Pediatrics. “We know how exhausting parenting can be, so it is important that we optimize and protect kids as best we can from SIDS and other sleep problems.”

The Centers for Disease Control and Prevention estimates 3,500 infants die annually in the United States from sleep-related conditions, which include SIDS, and a separate condition that doctors call ill-defined infant death. Also on that list are accidental suffocation and strangulation during sleep.

Suffocation or strangulation can occur as a result of bedding or clothing accoutrements — crib bumper-padding, blankets, pillows, stuffed toys and complicated garments. Blankets generally are not needed when a baby is sleeping, Bernstein said, because of the potential for overheating.

If a blanket must be used, he added, it should be thin enough to see through. Babies should never sleep on a couch or other soft surface, Bernstein and academy policy-experts say.

The number of infant deaths caused by SIDS initially decreased in the 1990s after a national safe-sleep campaign, but has plateaued in recent years, according to the American Academy of Pediatrics.

SIDS can occur during day or night sleep, but for reasons that remain unexplained, more babies die at night.

The new sleep guidelines, and an accompanying technical report, will be formally published next month in the journal Pediatrics. The policy includes new evidence that supports skin-to-skin contact for newborn infants — moms holding and breast-feeding babies within an hour of birth.

“Breast-feeding is an important protection against SIDS,” said Dr. Robert Glatter, a specialist in emergency medicine at Lenox Hill Hospital in Manhattan. “But at the same time, it’s vital to move the baby to a separate sleeping space, ideally a crib or bassinet in the parents’ bedroom, after completion of feeding.”

Dr. Leonard Krilov, chairman of pediatrics at Winthrop-University Hospital in Mineola, said the quest for SIDS’ cause has been exhaustive, and doctors have left few stones unturned. Clues, nevertheless, have remained elusive for a condition once called crib death.

“It remains unknown whether it is a neurological or structural issue,” he said Friday, noting that “there is some evidence that there is an environmental component, such as cigarette smoke.”

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An otherwise silent viral infection also has been proposed as a cause, Krilov said.

Beyond those findings, scientists are left with statistical data, which show that 20 years ago SIDS affected 130 babies per 100,000 live births, but now affects about 40 per 100,000, he said.