Chelsea Cuthbertson, 28, told a court how she went out to smoke cannabis and returned to find her son Malakai Watts’s face turning blue.
She denies deliberately killing the boy, despite experts claiming the damage to his head and his eight fractured ribs were most likely caused by a ‘non-accidental injury’.
Malakai was found ‘grey from head to toe’ when police arrived at the family’s two bed flat on February 2, 2019, after Cuthbertson dialled 999.
He was rushed to hospital from the home in Hythe, near Southampton, Hampshire, but died four days later after he was taken off life support.
Cuthbertson told the murder trial at Winchester Crown Court how Malakai and his twin had been asleep when she woke up that morning.
She said she still remembers ‘every minute’ of that day – from going outside to smoke cannabis to coming back in to wake her children for their morning feed and finding Malakai blue in the face.
Cuthbertson said she went outside and shut the door while she smoked a joint for about 15 minutes, but believed she would have been able to hear the babies if they cried.
The court heard how she told police she had gone outside for a cigarette because Dell Watts, Malakai’s father, told her to ‘say we don’t smoke weed’ if any professionals came to the home.
When she went back in Cuthbertson said she saw ‘straight away’ that Malakai’s face was blue, picked him up and called 999.
She was instructed how to give the baby CPR over the phone by the call handler.
Cuthbertson added: ‘I was distraught. I have never seen a child blue before.. I have never given CPR to anyone let alone a baby.
‘That whole day was just crazy, that morning when I had to do the CPR. It felt like a lifetime.’
The jury previously heard how Mr Watts told police he had taken cannabis and cocaine and had drank beer the day before Malakai was will, while Cuthbertson had drunk some wine.
He said that they had woken up to feed Malakai at 4am and that he went back to sleep in the lounge because he could tell his partner ‘was going to get angry and argumentative’.
Mr Watts, who worked as a car valet in Eastleigh, left for work and arrived at 8.30am, about an hour before Cuthbertson dialled 999.
The trial continues.