The evidence has become quite clear: bed sharing, or co-sleeping, increases the risk of sudden infant death syndrome (SIDS).

The latest study to reinforce the risk of bed sharing comes out of the UK (with contributions from New Zealand and Germany). Published in the British Medical Journal, Bed sharing when parents do not smoke: is there a risk of SIDS? An individual level analysis of five major case–control studies, combined data from five separate case-control studies on SIDS, creating a data set of 1472 SIDS cases to compare with 4679 healthy babies—the largest data series on SIDS that has ever been collected. The authors were able to separate out the effects of bed sharing along with other SIDS risk and protective factors to determine the risks of SIDS for families who only bed-shared, versus those who combined bed sharing with breastfeeding, smoking, and alcohol use. Other factors like the baby’s age, birth weight, and sleep position were also included. Their results are statistically strong, and show large big effect sizes.

Infants who share a bed with their parents during the first 3 months of life increase their risk of SIDS by five times—even if parents don’t smoke, don’t use alcohol, and exclusively breastfeed. In other words, breastfeeding and other positive SIDS risk factors avoidance does not erase the increased risk of SIDS associated with bed sharing.

In the combined data, 22.2% of babies who died of SIDS versus 9.6% of controls shared beds with their parents. The risk was especially high when other risk factors were present: bed sharing among infants whose parents smoked led to a 65-fold increase in SIDS; if parents consumed alcohol, the risk increased 90-fold. The risk of SIDS was “inestimably large” for bed-sharing if the mother used illegal drugs. But, again, even if none of these other risks were present, there was still a very large increase in SIDS rates. Bed sharing, even among breast-fed babies with no other risk factors, increased the risk of SIDS by a 5-fold compared to babies who slept on their own surface in their parents’ room or in their own rooms.

The American Academy of Pediatrics has recommended against bed sharing since their 2011 recommendations for the safest sleep environment for babies. Their guidelines are comprehensive and well-referenced, including many specific recommendations:

• Babies should be put down to sleep on their backs. (That doesn’t mean they must be kept on their backs. Once they can roll, let them roll. Do not use devices that force your baby to stay in one position. Baby sleep positioners kill.)
• Infants should sleep in a crib or bassinet—on a firm flat surface that’s safety-approved for infant sleeping. Car seats and other devices that hold baby in a sitting or semi-sitting position are not for routine sleep. (Which means that Fisher-Price Rock’n- Play Sleeper is specifically contraindicated for sleeping.)
• Room sharing without bed sharing is recommended.
• Avoid pillows, quilts, comforters, sheepskins, and other soft surfaces under the infant or in their sleep environment.
• Avoiding smoking, alcohol, and illicit drug use during and after pregnancy.
• Breastfeed
• Consider offering a pacifier at sleep times.
• Avoid overheating.
• Immunize infants according to the established recommendations of the AAP and CDC (that is, don’t use one of the made-up schedules that have no scientific backing.)

Bed sharing is a choice that many families make. Some parents enjoy the closeness of baby, and feel more secure; some nursing moms feel that it makes nursing easier. But parents who choose to bed-share should have honest, well-researched information on both risks and benefits. Bed sharing, even with no other risk factors, dramatically increases the risk that your baby will die of SIDS.

Roy Benaroch is a pediatrician who blogs at The Pediatric Insider. He is also the author of Solving Health and Behavioral Problems from Birth through Preschool: A Parent’s Guide and A Guide to Getting the Best Health Care for Your Child.