Some mothers find it hard to abide by the “Back to Sleep” rule for their babies. (ALAMY)

By the time new parents take their babies home from the hospital, they have been thoroughly drilled on the litany of infant-sleep no-nos: No stomach-sleeping. No loose blankets. No pillows. No soft mattresses. No crib bumpers. The list goes on.

Whether parents choose to follow these rules is another matter.

When her twins were born in 2008, Amy Cress of Silver Spring dutifully put her babies on their backs to sleep. But at about 6 months of age, her son Nathan rolled onto his stomach during the night. Cress was so relieved that her son was asleep, she left him like that. He preferred sleeping on his stomach from then on.

“We used bumpers, too, which is really not allowed,” she says. “We felt like rebels.”

It has been 20 years since the American Academy of Pediatrics (AAP) first recommended that parents place their babies on their backs to sleep for the first year of life to prevent sudden infant death syndrome, or SIDS. The rate of SIDS in the United States has plummeted more than 50 percent since the government launched its “Back to Sleep” campaign in 1994. In 2006, 2,327 infants died from SIDS in the United States.

Still, about 25 percent of U.S. babies sleep on their stomachs or sides, according to a national infant sleep position study. (In 1992, before the “Back to Sleep” campaign, that proportion was roughly 85 percent, according to the study.)

Like Cress, many parents find that infants sleep better and longer on their stomachs. New babies startle easily while on their backs and can wake themselves up frequently. Swaddling them can help prevent this, but wrapping a crying baby like a burrito isn’t always easy for a sleep-deprived parent in the middle of the night.

For some parents, there’s also a credibility issue. Despite the correlation between back sleep and the drop in SIDS deaths, scientists still don’t know the precise cause of SIDS. In fact, SIDS is by definition a death without a known cause, or, as the Centers for Disease Control and Prevention defines the syndrome, “deaths in infants less than 1 year of age that occur suddenly and unexpectedly,” and whose causes “are not immediately obvious prior to investigation.” Moreover, changing recommendations — between 1992 and 2000, the AAP said that side-sleeping was a safe alternative to back sleeping — make some people skeptical of the experts.

Other parents worry that babies will get flat heads from sleeping on their backs or will be delayed in reaching such milestones as rolling over.

Marian Willinger, who runs the SIDS research program at the National Institute of Child Health and Human Development in Bethesda, concedes that back-sleeping babies might have such delays; they might also learn to crawl later than stomach-sleepers. But by 18 months of age, there is no difference between the two groups, she says. Back-sleeping babies might also develop flat spots on the back of the head, but parents can help prevent it by repositioning the baby’s head during sleep and by having the baby spend time on his or her stomach during the day, she says.

Meanwhile, research on the cause of SIDS continues. Some studies have pointed to risk factors such as prematurity or exposure to secondhand smoke. Willinger and her fellow researchers are looking at defects in neurotransmitter pathways in the brain as a possible cause. SIDS victims seem to have had pathway deficits in brain regions that control automatic functions such as breathing, heartbeat, blood pressure, body temperature and arousal from sleep.

“Part of the problem is that you find a baby dead with no history of disease, so we’re starting at the end,” she says.

Other sleep-related deaths are more easily understood, such as accidental suffocation or entrapment due to pillows, quilts, crib bumpers or sharing a bed with a parent. Last year, the AAP revised its sleep recommendations in response to a rise in the number of infant deaths attributable to accidental suffocation and strangulation in bed, which more than quadrupled (from 103 to 513) between 1984 and 2004. The new rules take into account a child’s “total sleep environment,” which includes not only back sleep but also soft bedding, whether a child is breast-feeding, incomplete immunizations, bed-sharing, overheating and exposure to maternal smoking, alcohol and illicit drug use.

Reston pediatrician Ruth A. Mann says she gets more resistance to the AAP guidelines from parents who want to share beds with their babies than from those who insist on letting their infants sleep on their stomachs. It is common for some of her Indian, Pakistani and other Asian families to allow their babies to sleep with their parents or grandmothers. They’re not always receptive to changing that tradition.

“It can be frustrating,” Mann says. “Every parent is concerned about the well-being of their child, and they want the best.”

She understands the temptation to break the sleep rules. Some babies, newborns especially, sleep best when snuggled up next to Mom and Dad, under blankets or on their stomachs. It can be difficult to put the baby down in the bare-bones sleep environment prescribed by the AAP, especially a baby who is crying.

“It definitely is less convenient when you’re a tired mom,” she says.

Some mothers bring their babies into bed for breast-feeding and fall asleep, or they want to cuddle. Parents who live in neighborhoods with high crime rates often want to protect the baby by bed-sharing; others can’t afford a crib. The most recent AAP sleeping statement suggests room-sharing, with the baby in a crib or bassinet but close to the parents, as opposed to sharing their bed. Co-sleeping — an umbrella term that can mean either room- or bed-sharing — has become an especially controversial issue: Milwaukee ignited the blogosphere when the city’s health department launched an ad campaign last fall showing a baby sleeping in an adult bed next to a knife.

Despite all the warnings, Anya Levinzon, a photographer in Silver Spring, allows her infant daughter, Anara, to sleep on her stomach and in the family bed. But this information is not always well received by her peers. Once, she says, she brought it up when someone in her new mother’s group complained about having a gassy baby.

“I suggested you could put the baby on its belly,” she recalls. “They listened to me, but I don’t think they took me seriously.”

Many parents save such discussions for their closest friends and relatives or online forums where they can remain anonymous. In February, when Rebecca Woolf of the “Girl’s Gone Child” blog announced that she lets her babies sleep on their stomachs, nearly 150 commenters weighed in: supporters (“If it’s working for you, if it’s working for your baby, it’s right”), detractors (“I don’t [high-five] people for doing things that willfully put their kids in danger”) and empathizers (“My second child totally slept on her stomach from early on and I didn’t [breathe] a word to anyone”).

This discussion “shouldn’t be taboo,” Willinger says. People “should be able to talk to their doctor about why they’re having difficulty and get some advice.” Still, Willinger urges parents to consider the high correlation between the decrease in SIDS fatalities and the increase in back-sleeping infants. Every country that has recommended that parents place their babies on their backs to sleep has seen a 50 to 70 percent decrease in SIDS cases, according to Willinger. “When you think about it in terms of the life of your child, it’s a short interval, but it’s a critical one,” she says.

Indeed, the “Back to Sleep” campaign might be a victim of its own success: Many parents, such as Levinzon, don’t know anybody who has lost a baby from SIDS.

“Maybe if I did it would be a different story,” she says.

Saslow is a former Washington Post staff writer.