Researchers have new information about the possible health risks of infant co-sleeping, finding that it can increase the number of times the babies' oxygen level drops in the night and can cause them to rebreathe air they've already exhaled.
But most of the babies in the small study were able to cope with those changes.
"The bed-share infants experienced more desaturation events and were more often exposed to rebreathing," said Sally Baddock, an associate professor of midwifery at Otago Polytechnic in New Zealand. "But these infants, [who were] at low risk of SIDS [sudden infant death syndrome], appeared to be able to respond effectively and remain safe."
In the New Zealand-based study, published in the journal Pediatrics on Monday, Baddock and her colleagues used infrared video to monitor 40 healthy infants who were between 0 and 6 months old and who regularly shared a bed with at least one parent for five or more hours a night. They compared those infants to 40 babies who slept alone in cribs.
Overall, the bed-sharing infants experienced more oxygen desaturations throughout the night.
Oxygen desaturation refers to a drop in the level of oxygen carried in the blood, Baddock explained, and brief, mild episodes are common in healthy infants, but can become dangerous when they are more severe. Such episodes might occur more frequently when infants sleep in a bed with a parent because the environment is warmer, she said.
The bed-sharing infants also experienced more episodes of carbon dioxide rebreathing, or breathing in the same air that they had let out. Those events were often related to the presence of bedding or parents' clothing.
"For example, if your head is under a blanket, you may be breathing the same air in and out over time. This will mean the air will come to contain increasing levels of carbon dioxide and decreasing levels of oxygen," Baddock said.
Although rebreathing can be dangerous, the babies in the study seemed to increased their breathing in order to keep their oxygen levels within the normal range, Baddock noted. The authors of the study also point out that "mothers also spontaneously remove bedding during head covering events."
Indeed, the study suggests that infants and parents who shared a bed did what they needed to do to stay safe. But it also makes it clear that co-sleeping is a potential hazard, particularly for babies who live with a current smoker or whose mother smoked during pregnancy. Parental alertness is also key: Adults who are unresponsive -- because of alcohol consumption, for example -- could put their infants at particularly high risk by not helping to prevent rebreathing.
"I think the message is a fair one," said Dr. James McKenna, head of the Mother-Baby Behavioral Sleep Lab at the University of Notre Dame. "They argue that it is not enough to simply judge a practice like bed-sharing as being simply 'dangerous' before determining what kind of bed-sharing is involved and who is involved."
The difficulty may be in knowing which infants are possibly at greater risk.
"We just go with, in general, there shouldn't be any bed-sharing," said Latoya Bates, director of the Center for Infant and Child Loss at the University of Maryland School of Medicine, who explained that bed-sharing can increase the risk for sudden infant death, accidental suffocation, wedging and entrapment. "Who's to say which babies it's good for?"
The American Academy of Pediatrics recommends room sharing with infants, but not bed-sharing. In particular, it advises against bed-sharing when babies are younger than 3 months or when parents are excessively tired or have consumed alcohol or medication. It also points out that bed-sharing is particularly bad for babies whose parents are smokers.
But despite such concerns, many parents continue to share a bed with their infants, arguing that it helps promote breast-feeding and skin-to-skin contact. The authors of the new study argue that makes it paramount there be more research into whether any specific conditions or physiological reactions put some babies at greater risk than others.
"As bed-sharing is a practice valued by many families, it is important to understand [those] situations when it is unsafe," Baddock said.