Sharing a bed or even a couch with a young infant may increase the risk of sudden infant death syndrome (SIDS), according to a new study.

While experts cannot predict SIDS, risk factors include bed sharing with a parent who smokes. This study suggests that bed sharing, even with nonsmoking parents, also increases the risk of SIDS in infants less than 11 weeks old.

SIDS is the leading cause of death among infants 1 month to 1 year old. The highest number of SIDS cases occur from 2 to 4 months; 91 percent of cases occur between 1 and 6 months of age, according to the American Academy of Pediatrics.

Although the cause of SIDS is unknown, placing an infant to sleep on his or her stomach, exposure to smoking, and use of soft pillows or bedding have been identified as major risk factors.

Researchers say the results of this study show that sharing a couch to sleep, sleeping in a room alone, and sleeping in bed with parent are also associated with an increased risk of SIDS.

"The safest place for your baby to sleep is in a cot [crib] in your room for the first six months," states researcher David Tappin, MD, MPH, of the University of Glasgow, in a news release.

In the study, which appears in the July issue of The Journal of Pediatrics, researchers evaluated 123 SIDS cases in Scotland from 1996 to 2000.

The parents of the infants provided information about the infant's daily routine, such as where they normally slept, and the circumstances of their death. Researchers then compared this information with the habits of 263 healthy babies.

The study showed that there was a link between SIDS, bed sharing, couch sharing, and the location of the infants when they died, especially among infants less than 11 weeks old, regardless of how long they shared the sleeping space or their exposure to smoke.

The results showed that only 11 percent of the infants were reported to routinely sleep in their parents' bed compared with only 5 percent of healthy babies.

They also show that more than half (52 percent) of the SIDS babies had shared a bed/cot/couch or other surface at some point during the day or night that they died. Within the healthy babies group only 20 percent shared sleeping space with a parent during their last sleep.

Read WebMD's "Preventing SIDS: New Advice for Parents"

Bed Sharing Raises SIDS Risk Threefold

Of the SIDS infants who shared a bed during their last sleep, 87 percent were found dead in their parents' beds.

Sharing a sleep surface was associated with a nearly threefold increased risk of SIDS.

Researchers say the relationship between bed sharing or couch sharing and SIDS was especially strong among infants less than 11 weeks old, regardless of maternal smoking. The risk remained high with SIDS for breastfeeding mothers who shared a bed with infants.

Seventy-two percent of the SIDS infants who were found in their parent's bed were less than 11 weeks old.

Researchers say sleeping between parents may put extra stress on the infant and could put the baby too close to or underneath pillows or blankets.

Although previous studies have linked sleeping in a separate room with a higher risk of SIDS among very young infants, this study showed sleeping in a separate room did not increase the risk of SIDS unless the parents were smokers.

Read WebMD's "Test During Pregnancy May Predict SIDS Risk"

Bed Sharing and Breastfeeding

Researchers say some breastfeeding advocates promote bed sharing as a breastfeeding aid and have pointed to research that shows bed sharing raises the risk of SIDS only if the parents smoke.

However, this study showed that there was an increased risk of SIDS among babies who were breastfed, even among nonsmoking parents.

In an editorial that accompanies the study, Bradley Thatch, MD, of Washington University of Pediatrics, writes that the bed sharing controversy will continue but this study provides much needed scientific evidence for the ongoing debate.

The American Academy of Pediatrics recommendations on safe sleep practices for infants include:

— Always put healthy babies to sleep on their backs for naps and at bedtime.

— Avoid overheating: Never cover baby's head with a blanket, keep room temperature at 68 degrees to 72 degrees F, and do not overdress baby.

— Do not have more then one baby per crib.

Read WebMD's "Swaddling Newborns May Help Them Sleep"

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Tappin, D. Pediatrics, July 2005; vol 147: pp 32-37. News release, American Academy of Pediatrics. American Academy of Pediatrics: "Reducing the Risk of SIDS in Childcare."