Three-week-old Harvey McGlinn couldn't be revived after his mother Tattika Dunn unwrapped his cloth sling and found him pale and motionless at the Central Coast's Long Jetty Community Health Centre on April 8, 2019.
An inquest into his death, which began on Monday, will examine his cause of death, whether NSW parents are receiving adequate advice on baby slings and whether changes are needed.
While in the sling hung from Ms Dunn's neck, Harvey had no part of his body exposed and was at times horizontal and below his mother's belly button, witnesses told the NSW Coroners Court.
"It was all like an envelope or a pouch," nurse Kathryn Mitchell said.
Still, she wasn't concerned when she saw Ms Dunn in the waiting room and called her in for a scheduled health check at 9.05am.
Harvey wasn't making any noise and moving but Ms Mitchell said she'd assumed the boy had fallen asleep and been placed horizontally by his mother when she sat down in the waiting room.
In the consultation, the woman discussed feeding, sleeping and other issues for 10 to 15 minutes before Ms Mitchell asked to examine Harvey.
That revealed he had become pale, blotchy and grey and had fresh blood coming from his nose.
Harvey's head and neck were curled to such a degree his chin was "right up against" his chest, Ms Mitchell said.
"I thought either he was unconscious or dead," the nurse told the court.
Despite immediate resuscitation efforts and a rescue helicopter from Sydney being scrambled, the boy was declared deceased at 10.12am.
The devastated mother collapsed in the clinic. She declined to be involved in the inquest, but there's no suggestion of criminality or breaching her duty of care.
"His death was completely unexpected and very shocking," counsel assisting the coroner Jake Harris said.
He said an expert medical report had found Harvey very likely accidentally suffocated in the baby carrier, with his light weight potentially increasing his vulnerability to poor positioning.
A 2015 French study of 19 infant deaths in soft adult-worn baby carriers and slings had recommended they not be used before the child is four months old.
But the expert suggested bans may go unheeded and educating parents was a more effective method.
Since Harvey's death, staff in Central Coast Local Health District have started adding baby carrier advice to discussions about sudden unexpected death in infancy and sudden infant death syndrome.
TICKS (Tight, In view, Close, Keep chin off chest and Supported) advises parents ensure the baby is held tight and high; is in view of the parent at all times; is close enough to kiss; is in a position so their chin is off their chest and never curled; and that their back is well supported and in a natural position.
Alarm bells now ring in Ms Mitchell's head when she sees new parents with slings, she said.
"I don't encourage anyone to use them," she said.