The woman, who has interim name suppression, pleaded guilty at a hearing before Judge Duncan Harvey.
The summary of facts says the baby was born premature and had only been home a matter of weeks when it lost consciousness for the first time.
At the time the woman’s partner woke her up with the baby in his arms "cold and floppy".
Text messages between the couple early the following day revealed that the father was not at the home when the woman said she needed to take the baby to hospital.
At one point she dialled 111, but hung up before getting put through.
In a statement to police, the defendant said that when the man had passed her the baby after telling her it had stopped breathing, the baby looked fine to her and "was drinking and everything fine ... I just presumed what had happened was not as bad as [the father] had described".
In the following days, medical professionals including a general practitioner, Plunket nurse and a midwife visited the home but the woman said nothing to them about the incident.
The defendant did not take the baby to hospital despite knowing it needed to go to hospital, the summary said.
When the baby was 5 weeks old, ambulance staff uplifted it from the home.
When the baby was rushed to hospital, it had a heart rate of zero, its skin was cyanosed (a blueish discolouration), its temperature was 33.7degC and it had to be resuscitated by medical staff, the summary of facts says.
The baby was flown to Auckland's Starship Hospital to be treated.
Dr Patrick Kelly, the service clinical director at Starship Hospital said the baby "came about as close to death as it is possible to come and still survive".
A full medical examination revealed the baby had two broken ankles, broken bones at both knees, two broken wrists, multiple fractures of left ribs, possible fractures of the right toe and an unexplained abdominal injury.
Buckling of the ribs on the baby’s chest could be attributed to being given CPR, the summary says.
"The medical report concluded that the only possible diagnosis in this case is of non-accidental injury from repeated episodes of physical child abuse and that the cause of the stopping on the breathing was most likely from inflicted suffocation."
Rib fractures were as a result of violent squeezing of the chest and other fractures as a result of forces applied to the baby as it was twisted and pulled.
A police investigation revealed no evidence suggesting any person other than the woman or her partner could be responsible for the injuries.
The woman was remanded on bail and is due to appear for sentencing on April 14.
