SINGAPORE - A woman, who was the primary caregiver of her seven-year-old autistic son, pushed him out the kitchen window of their ninth-floor Tampines flat after she was seized by thoughts that he was the reason for her exhaustion and marital problems.

On Friday (March 18), the 43-year-old woman was sentenced to five years' jail after she pleaded guilty to a charge of culpable homicide not amounting to murder for killing the younger of her two sons in September 2014, one day before her 42nd birthday.

A gag order on the name of the dead boy was made by district judge May Mesenas in September 2014 when the woman was charged.

On Friday, the High Court heard that the woman, who has a history with the Institute of Mental Health since 2008, had suffered a relapse of her major depressive disorder.

Her husband and older son, who wrote letters pleading for leniency, were not in court on Friday.

In sentencing the woman, Justice Tay Yong Kwang noted that "far from being angry" with her, her husband and son longed for her return to the family.

He took into account that her mental condition had improved while she was in custody, that there was a low risk of of her re-offending, and that she had readily admitted what she had done.

"I hope you recover well and that you can return home much stronger emotionally to rebuild your family and personal life," said Justice Tay.

The court heard that the woman, an education manager at a cosmetics company, woke up at 4.30am on Sept 13, 2014, to do household chores.

She was in a cold war with her husband and the tiff escalated when she shouted at him to bring in the laundry as it was raining. He threw the laundry poles on the floor before leaving the flat with the older son. She went on to clean up her younger son, who had defecated in his trousers, and took a rest.

After some time, she felt that he was the reason for her exhaustion and problems and decided to kill him. She coaxed the boy to a stool at the kitchen window and told him to look down to find his grandmother. When he did so, she grabbed his calves and pushed him out. The boy died from multiple injuries from the fall.

Asking for a jail term of not more than five years, the woman's lawyer, Mr Anand Nalachandran, noted that she sacrificed her own well being for the needs of the family and was stretched to breaking point. Before the incident, she did not lay a hand on her son, he noted.

Deputy Public Prosecutor Krystle Chiang, seeking five to seven years' jail, said that while this was a tragic case, there was an element of premeditation against a vulnerable victim.