Since 1994, doctors have been advising parents to lay babies down to sleep on their backs in an effort to prevent sudden infant death syndrome, or SIDS. By all accounts, the Back to Sleep campaign has been a major success, cutting the SIDS death rate in the U.S. in half.

But since 2000, death rates have plateaued, prompting experts to shift their focus to other risk factors associated with SIDS. A recent study found that even after the Back to Sleep campaign, 99 percent of SIDS cases involved at least one of the identified risk factors, and despite the drop in death rates, the average number of risk factors per SIDS death has not declined.

“The really important recommendation out of our study is that caretakers concentrate not on avoiding a single risk factor — such as putting the baby to sleep on its stomach — but rather avoiding multiple risk factors,” said Dr. Henry Krous, director of the San Diego SIDS Research Project at Rady Children’s Hospital-San Diego. “These risk factors are additive. The more risk factors, the higher the likelihood the baby is going to die.”

SIDS is by definition a diagnosis of exclusion. Medical examiners will label a sleeping baby’s death as SIDS if no other explanation is offered by the autopsy, death scene investigation and subsequent lab tests. Over the years, researchers have identified several risk factors — including sleeping face down, bed-sharing, sleeping on an adult bed, premature births and parental smoking — that occur frequently in SIDS cases.

Krous and other researchers with the San Diego SIDS Research Project reviewed the 581 SIDS deaths in San Diego from 1991 to 2008 to examine what risk factors were involved and how their prevalence changed after the Back to Sleep campaign. As expected, the number of babies who had been put to sleep on their stomachs had dropped from 85 percent in 1991-93 period to 30 percent in the 1996-2008 period.

But the researchers found that other risk factors increased in prevalence among SIDS cases over that same period. The percentage of infants sharing a bed increased from 19 percent to 38 percent, sleeping in an adult bed from 23 percent to 45 percent, and those born prematurely from 20 percent to 29 percent of cases.

Overall the death rate from SIDS has dropped from 1.34 per 1,000 live births in 1991 to 0.64 in 2008. Further progress may depend on getting parents to pay attention to more of those risk factors, as well as to get more parents on board with Back to Sleep. Even in the post-Back to Sleep era, 30 percent of SIDS babies were still put to sleep on their stomachs, and nearly half of SIDS babies were found on their stomachs.

“There is certainly no reason,” Krous said, “why we shouldn’t be able to expect a lowering of the SIDS rates from their present levels with a wider adoption of these Back to Sleep recommendations.”

Nearly all SIDS cases involved at least one identified risk factor. On average, each SIDS death was associated with three risk factors. So researchers believe that by eliminating all known risk factors, SIDS deaths could be driven to an almost imperceptible level.

“I think that’s theoretically possible,” Krous said. “Although there are a few babies who don’t have any risk factors that still die. We need to know more about it.”

Triple-risk model

Experts believe that SIDS occurs when three factors intersect: age, external risk factors and internal vulnerabilities. The majority of SIDS cases occur between the 2nd and 4th month of life.

“That’s a period of time that a baby’s physiology is changing quite rapidly and its growth, particularly its brain, is growing quite rapidly,” Krous said. “During sleep, this is an inherently unstable system.”

External risk factors are those parents are able to control, such as bed-sharing, tummy sleeping or cigarette exposure. A third element is an underlying vulnerability of the baby itself, an abnormality that the baby is exposed to or developed as a fetus.

Research suggests the most important of these abnormalities may be a deficiency in the neurotransmitter serotonin. That could prevent the body’s warning systems from waking the child when it detects high levels of carbon dioxide in the blood. Instead of waking, the baby slowly asphyxiates.

“When each of these three elements intersects simultaneously, that’s when we think SIDS will occur,” Krous said. “We need to figure out why those babies are still dying if they don’t have all three of those elements impacting at the same time. We haven’t been able to answer that question yet.”

The Back to Sleep campaign, while a great success, has also highlighted how much more clinicians still don’t know about SIDS.

“If you’re getting a significant number of infants alone in the crib, dying face up, you still haven’t answer the question about eliminating risk factors,” said Dr. Clifford Nelson, deputy state medical examiner in Oregon. “There’s something else going on you can’t account for.”

Nelson said the total number of infant deaths has dropped and SIDS deaths as a percentage of total infant deaths is dropping as well. Part of that is the focus on eliminating risk factors. But medical examiners are also getting better at identifying the actual causes of death that might have otherwise been categorized as SIDS. When deaths can be linked to a cardiac rhythm abnormality or a metabolic problem, those cases are not longer classified as unexplained, no longer tallied as a SIDS death.

“We’re finding things that are preventable and we’re able to identify things that are very strong risk factors,” Nelson said. “As those are continued to be identified, as they’re able to be treated or you eliminate the risk factor, then the total number of deaths is going to go down.”

Parental guidance

Researchers must tread carefully, he said, to avoid suggesting a causal link between risk factors and SIDS before they are scientifically established.

“Because sometimes when you put out recommendations, some people get hurt by them,” Nelson said. “You may be offending somebody’s cultural norms or you may be offending somebody by placing blame on them for having done something that really you can’t say for certain caused something.”

And even the Back to Sleep recommendation has downsides. Pediatricians have noticed that children sleeping on their backs tend to develop motor skills a little later and can develop flat spots on the backs of their heads. Some studies have suggested that children don’t sleep as well as on their backs, leading to potential sleep issues as they grow older.

Krous doesn’t believe those drawbacks are an unavoidable consequence of sleeping face up. Pediatricians now counsel parents to give babies plenty of tummy time while they’re awake. And while babies may lag in motor development when sleeping on their backs, it tends to result in earlier cognitive development. Issues with motor development or flat spots can usually be easily remedied once the child is older than the age when SIDS typically occurs.

“I think it’s definitely a risk that’s well worth taking when you look at the dramatic effect that Back to Sleep has had on the incidence of SIDS,” said Dr. John Evered, a neonatologist at St. Charles Bend.

The strength of the Back to Sleep campaign, however, may have been its simplicity. The message was simple and it was easy for parents to implement.

“I don’t think there’s anything simpler than Back to Sleep,” Evered said. “It even comes with its own catch-phrase.”

Those counseling new parents must now find ways of expanding that message without losing its jingle-like effect.

“Our main message for safe sleep is face up, face clear, smoke free and baby near,” said Cynthia Ikata, a nurse consultant in the Oregon Office of Family Health.

Ikata said state officials provide educational materials for hospitals and clinics to help counsel new parents about the risk factors of SIDS, and nurses convey safe sleep practices during one-on-one conversations with families.

Oregon SIDS rates have declined along with national averages, although the smaller numbers of SIDS deaths in the state make it difficult to identify recent trends. Nationally, about 1 in 2000 babies die of SIDS and researchers like Krous believe that rate can be lowered.

“We want to do everything we can to maximally reduce a baby’s risk of dying of SIDS,” he said. “It’s an uncommon event. But for the family that’s stricken by it, it’s all or none. It’s a horrible thing to go through.”