A six-day-old baby is carried inside the SlingRider. Critics of the bag-sling design say newborns cannot be easily monitored because they're not visible in the bag. (M'Liss Stelzer)

The risks of a bag-type sling similar in design to the Infantino models recalled last week after the deaths of three infants have been known for years, say sling advocates and designers.

Infantino, based in San Diego, Calif., recalled its SlingRider and Wendy Bellissimo models after the suffocation deaths of three newborns in 2009. The U.S. Consumer Protection Safety Commission warned in an advisory earlier this month that newborns were at particular risk.

The Infantino designs are actually described as "bag slings" and are not slings in the traditional sense, said Susie Spence, a volunteer and past president of the community group, Babywearing International of Birmingham, Ala. "Baby-wearing" advocates endorse attachment parenting, or keeping a baby in close bodily contact.

There are two problems with bag slings, she said. Babies placed inside the slings easily roll so that the mouth and nose are pressed against the sling and the adult's body, potentially blocking breathing. As well, babies also tend to slide into a C-shape position, where the infant's chin is pressed into its chest, posing a risk of something called positional asphyxiation.

"The reason that the baby-wearing advocates have been vocal about this product was that the design flaws and the risks were identified and then that's exactly what happened," said Spence, of the infant deaths, which occurred in the U.S.

"The other thing about this SlingRider is that no amount of education could solve the problem. It can't be made safer. An educated user cannot position the baby correctly in it," said Spence. "It's constructed more like a duffle bag with a harness."

M'Liss Stelzer, a New Mexico nurse, uses a doll to show how a baby's face can be covered in a bag sling. (M'Liss Stelzer)M'Liss Stelzer, a New-Mexico-based nurse who also runs baby-wearing workshops, was the first to raise red flags around the Infantino SlingRider in 2006, three years after it hit the market.

Stelzer said she became aware of the problems after parents came to her workshops with the Infantino sling, saying they were having trouble settling the baby in it. Stelzer noticed that babies carried in the sling appeared to be labouring to breathe.

Stelzer also noted that the baby was hidden from view in the carrier, preventing parents from easily monitoring an infant should trouble arise.

"Nobody walks around with a towel over your baby's face, but that's what the SlingRider does. If you look down, you cannot see a thing," said Stelzer.

She bought equipment to test the babies' blood oxygenation levels while they were in the sling and found that oxygen levels either fell, or that babies began breathing at a rapid pace to compensate.

'It's like putting a baby in a purse'

"I contacted Infantino and said, 'I'm really concerned about the design flaws in this carrier. It's really scaring me,'" she said, adding that she also sent her concerns to the CPSC as well.

"It's a scary product. It's not designed to hold your baby like you do in your arms. It's like putting a baby in a purse," said Stelzer.

All slings can pose risks to babies if they are not used properly, including the risk of the baby falling out or the risk of suffocation, said Spence. As slings have grown in popularity — promoted as a better way to bond with your baby — more sling designs have hit the market.

Bag slings tend to carry babies on their backs, something that infant educators say is a no-no. A well-designed sling should allow the parent to carry the baby in an upright position, tummy to tummy, with the baby's face resting in full view against the adult's chest, said Spence

Ottawa-based sling designer Corrine Mahar-Sylvestre said advocates of baby-wearing are thrilled to see the recall, but worry that designs similar to the Infantino style of bag sling continue to be sold at national retail chains.

"We're really happy that something is being done about this type of sling, but it's not just Infantino. A lot of companies have knocked off the Infantino," said Mahar-Sylvestre, who also owns Upmama.com, which sells a baby sling and sling-wear.

"This has been known for years in the industry," said Mahar-Sylvestre. "Baby-wearing manufacturers, retailers and educators have all been trying to get these out of the public's hands."

Mahar-Sylvestre voiced her concerns to Health Canada several times since 2008, even going so far as to offer her services as a sling-designer to the government agency. She has designed slings for several large companies.

Health Canada is currently working with the global standard firm ASTM International to develop a voluntary standard for infant slings.

Health Canada said in an email to CBC News that it "routinely consults with the Canadian public, industry, standards organizations … and other interested parties on matters relating to health and safety, including the development of standards. The department regularly conducts public consultation where anybody can submit comments."

Infantino did not return calls made by CBC News.