M'Liss is a former NICU nurse, mom to two, and an avid babywearing advocate and teacher. She's married these specialties and has been doing research on oxygenation levels in newborn babies. Part of this
research is mentioned about in the Babywearing Bliss primer, but she has continued to collect data, focusing more on what she is calling "bag" slings*.
Here is an excerpt from "Concerns About Bag Slings", taken with permission from the author.
First, the design of the SlingRider causes baby to naturally curl chin to chest, larger babies more so because their heads are positioned further up in the carrier. This position kinks baby’s airway causing the baby to work harder to breathe. (For more information on the importance of maintaining an infant's head and neck in an aligned position see the articles “Baby car seat ‘cot death’ concerns” and “Simple Car Seat Insert to Prevent Upper Airway Narrowing”.)
Now, the instructions for every Infantino front pack emphasize that baby should not be chin to chest (“Baby's chin should not point down toward baby's chest") and there are even diagrams of correct positioning. However, the SlingRider instructions omit this important detail and, not only that, but the product shots of the SlingRider contradict the information in the front pack instructions. Photos on Infantino’s website.
Second, it is very difficult to keep a newborn’s face away from the pouch fabric. The SlingRider is roughly triangle shaped; flat bottom and two sides that slant upwards toward the elastic top. This “triangle” means that the pouch fabric is always angled very close to the sides of baby’s face. If baby rotates even slightly he ends up with his nose within a ¼” of the side, or even pressed against the side of the pouch. Once baby has his head pressed against the side of the carrier and/or against the parent's body there is a risk of the baby suffocating or becoming oxygen deprived. (See SlingRider #1)
Third, it is very difficult for the parent to monitor their infant unless they pull
open the top of the sling. The SlingRider is deep, plus it sags when baby is placed in it, further increasing the depth of the carrier. The gathered top and the fact that the sling hangs so low obstructs the parent’s view of baby. If a newborn were to have difficulty breathing, and/or rotate until his nose and mouth was pressed against the side of the carrier, the parent may not be aware of the baby’s respiratory distress for some time. Compounding this problem is the impossibility of feeling the baby's distress through the thick fabric of the sling.
Sling tightened as far as possible. 5'3" mother.
6 pound newborn
8 pound newborn
Compare the SlingRider with a shallow fabric pouch or adjustable open-tailed sling (or mei tai or wrap). In these types of carriers an infant is easily monitored and visualized. Also, a newborn's head is effectively sandwiched between the sides of these carriers, preventing the infant from rotating his/her head into the sides of the carrier.
"I believe there are two significant features that distinguish the dangerous "bag sling" from a typical pouch.
First: The bag sling has a padded, structured bottom (in the area where the baby's body rests). Therefore the fabric that supports the baby cannot conform to the baby's body and it is almost impossible to position the baby diagonally across the fabric, for proper back and
head support. (Also, if the "safety harness" is used, it forces the baby into an improper parallel-to-rails position.) The padding also makes it nearly impossible to carry the baby snug against the wearer's body, because it creates a flat surface that resists being adjusted and tightened.
Second: The rails are padded and elasticized, so -- esp. in combination with the depth of the pouch -- the sides of the sling tend to "close up" over the baby, restricting the flow of fresh air, and preventing the wearer from being able to easily see and monitor her baby. (This is less of a problem with an older baby who is sitting more upright in the sling, of course.)
The third big difference between a "bag sling" and a regular pouch is one more of wearing comfort than of the baby's safety, and has to do with the difficult-to-adjust heavily padded strap that goes over the wearer's shoulder and back. By itself I don't think this is a major
safety issue, but in combination with the above features, it adds to the tendency of these slings to be too large and very difficult, if not impossible, to wear snugly and with the baby well positioned.
So, the problem is more or less a function of the way you put the baby in the sling, but the
issue with these bag slings is that, by their design, they encourage poor positioning."
-Holly McCroskey Lewis, co-leader of Bay Area Babywearers,mom-of-two (hollyml)