Liberal Leader Justin Trudeau and his wife Sophie Grégoire welcomed their third child Friday, and there was word the couple might share a bed with their newborn.

The baby boy, named Hadrian, joins siblings Xavier James, 6, and Ella Grace, 5.

At the Liberal convention last week in Montreal, just days before the baby was born, Trudeau told reporters that he and his wife were considering co-sleeping, a practice where parents share a bed with their infant that is also called bed-sharing. 

So what do experts say about those sleeping arrangements?

Government agencies in a number of western countries, including the U.K., Canada and the U.S., recommend infants sleep in cribs for the first year of life.

A study carried out by an international team of researchers and published last May in the British Medical Journal concluded that co-sleeping was a "significant" risk factor for sudden infant death syndrome (SIDS) for the first 15 weeks of life in "the absence of … all other risk factors."

Many mothers share a bed with their baby given the popularity of attachment parenting, which encourages co-sleeping and prolonged breast feeding.

Opponents, however, say sharing a bed comes with caveats:

  • The adult may roll over onto a sleeping baby.
  • The baby could be smothered by blankets.
  • Adult body heat may be too much for a baby, because newborns have a limited ability to sweat and regulate body temperature.

Despite recommendations for separation, Dr. William Sears, an American pediatrician and author of several parenting books, has taken a more flexible approach on the issue in his writings and with his own family.

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Some experts recommend infants sleep in cribs for the first year of life, despite the popularity of co-sleeping. (CBC)

He and his wife Martha's first three babies were easy sleepers, and they felt no need or desire to have them share their bed.

But their fourth child hated her crib and at times made life miserable for other family members. Finally, one night, his exhausted wife brought the baby into their bed, where they all slept better. Over the years, Dr. Sears observed several more of his children as they shared a family bed.

His hypothesis is that SIDS is a sleep disorder, primarily a disorder of arousal and breathing control during sleep.

"All the elements of natural mothering, especially breastfeeding and sharing sleep, benefit the infant’s breathing control and increase the mutual awareness between mother and infant so that their arousability is increased and the risk of SIDS decreased," he says on his website.

The Canadian Paediatric Society says parents who want to remain close to their newborns should "be aware that room-sharing is protective against sudden infant death syndrome and that this type of sleeping arrangement is a safer alternative to bed-sharing."

The society acknowledges, however, that no randomized studies can be performed to measure the potential impact of its sleeping environment recommendations for a reduction in the incidence of any sudden unexpected infant death.

The Public Health Agency of Canada recommends infants sleep on their backs, in a crib, to minimize the risk of SIDS.