The calming effects of swaddling might make it more difficult for some infants to rouse from sleep - raising the possibility that the practice could increase the risk of sudden infant death syndrome (SIDS), a small study suggests.

The study, reported in the Journal of Pediatrics, found that in 3-month-old infants new to swaddling, the practice seemed to reduce the brain response to an external stimulus - a puff of air delivered to the babies’ nostrils.

An infant’s ability to rouse from sleep in response to such conditions is believed to play a role in SIDS. The findings, therefore, raise the question of whether swaddling could, for infants new to the practice, increase the likelihood of SIDS, according to the researchers.

The potential role of swaddling in SIDS is controversial, with the few studies that have been done so far coming to conflicting conclusions.

On one hand, swaddling helps infants stay on their backs as they sleep, the recommended position for lowering SIDS risk. There are also some studies that show a lower prevalence of SIDS in cultural groups where swaddling is common.

However, some other studies have found that swaddled infants have no reduced SIDS risk, or even an increased risk. And one of the benefits ascribed to swaddling - sounder sleep - could be undesirable as far as SIDS risk; it’s thought that problems arousing from sleep in response to breathing disruptions or other stimuli contribute to SIDS.

For the new study, Australian researchers studied the physiological effects of swaddling in 27 infants using polysomnography, which monitors heart rate, breathing, electrical activity in the brain and other functions as a person sleeps.

The infants were studied when they were 3 to 4 weeks old, and again at the age of 3 months. Fifteen had been regularly swaddled at home since birth or soon after, while 12 had not. The researchers monitored each infant’s sleep when swaddled and when left unswaddled.

They found that among infants who were not normally swaddled at home, swaddling reduced brain arousal during sleep at the age of 3 months. The infants also showed less stability in their heart rate compared with when they slept unswaddled.

The same was not true of babies who had been routinely swaddled starting early in life, according to the researchers, led by Dr. Heidi L. Richardson of Monash University in Melbourne.

The findings suggest that decreased arousal during sleep may be less a result of swaddling, per se, and more an effect of an infant’s unfamiliarity with sleeping swaddled, the researchers write.

However, the effect seen in new-to-swaddling infants at the age of 3 months is important, Richardson’s team notes, because that is within the age range when SIDS risk is highest. They add that it is also the time point when many mothers return to work and leave their babies with a caregiver who may not be familiar with how the baby usually sleeps.

The researchers speculate that this could be a factor in the disproportionately high percentage of SIDS cases - 16 percent - that occur at child-care centers.

The question of whether swaddling does, in fact, increase SIDS risk in some infants requires further study, according to the researchers. It may turn out that, if parents wish to swaddle their infants, they should do so starting soon after birth, to avoid the potential risks from introducing it later, Richardson and her colleagues write.

For now, they say, the findings highlight the need for fully understanding the effects of swaddling before broadly recommending the practice for improving infants’ sleep.

SOURCE: Journal of Pediatrics, online March 15, 2010.