Cardiff Crown Court was told how Carol Stokes, 32, became pregnant by a friend after she and her lover, Colleen O'Neill, with whom she lived, decided they wanted a child together. But she allegedly drowned 16-month- old Lewis in a bath just a week after Miss O'Neill walked out on her.
Stokes, of Adamsdown, Cardiff,pleaded not guilty to murder, but guilty to manslaughter on the grounds of diminished responsibility.
Leighton Davies QC, for the prosecution, said: "These are tragic and bizarre circumstances. In 1994, she ... formed a relationship with Colleen O'Neill ... [then] they decided they wanted a child. During the pregnancy, but particularly after the birth, she suffered post-natal depression. She had even tried to electrocute Lewis and herself in the bath, but had failed."
Stokes carried out her threat a week after Ms O'Neill told her she was leaving. Mr Davies added: "She took her sleeping baby and submerged him in a half-full bath of water. He drowned but then, thinking he was still alive, she placed a length of rope around his neck and strangled him. She then dressed him and placed him gently on his bed before walking to the local hospital and telling staff what she had done."
"In the months leading up to the death she sought help and was seen by psychiatrists and social services on several occasions. She openly expressed urges that she wanted to kill herself and her child. But nobody believed her threats were serious, although Lewis was placed on the social services at risk register."
John Charles Rees QC, defending, said: "She sought help from professionals and was badly let down."