Mother-of-two Rebecca Wratten smothered her five-month-old-son after a bout of drinking vodka.
Baby Jordan had been asleep at the family home in Nansen Close, Ashby Fields, Daventry, when his mother put a cushion over his head.
She used such force she bent the chair he was sitting in.
The 22-year-old will be sentenced after admitting the killing before Northampton Crown Court this week.
She had been due to stand trial for murder, but the prosecution accepted her guilty plea to manslaughter.
The hearing was adjourned so reports on her can be prepared.Joan Butler, QC, prosecuting, said the cause of death was smothering.
Wratten had placed a cushion on the baby s head as he lay asleep in his baby chair. The pressure she applied was sufficient to bend that chair.
She added: It was long enough to stop the child from breathing.
Geoffrey Nice, QC, representing Wratten, said: Wratten accepts she placed the cushion on his face. She recognises that was capable of causing damage. She accepts death resulted.
The court was told Jordan, who had no other injuries, probably died between 11.45pm and 12.15am on the night of August 31 and September 1 last year.
That was the time when a neighbour heard two or three loud screams from Wratten.
Miss Butler said: Wratten rang the emergency services to say she thought her son was dead.
She was later to say: I did not mean to kill him. I am mentally f….d up. I don t know why. I did not intend to kill him. I just wanted help.
Miss Butler said the father of Wratten s two children was David Ryan. It was a stormy relationship.
At the time of Jordan s death, she was not suffering from post natal depression and the care she had been giving to her children did not give any cause for concern.But she had complained of feeling isolated and depressed and said the children would be better off without her.
Wratten also told police she began drinking a great deal a few weeks before Jordan s death but had cut it down. She was looking forward to starting a college course and had been enjoying working for an escort agency.
Outlining the fateful events on the night of August 31 and September 1, Miss Butler said Wratten had bought cigarettes and vodka.
She had got Jordan ready for bed. At 8pm she had spoken to David Ryan and told him everything was all right.Miss Butler said:
The child was asleep and remained asleep. There was no question of him being fractious. She continued drinking. She said she put a cushion over Jordan s head and held it down.
Jordan was asleep. She held it down for a little while and put pressure on it.