Leung Sin-ting, 27, befriended the pregnant woman identified only as "Ms Lee" through an online childcare forum in 2008, telling her she was expecting a baby boy.
She invited her to her home to pick up a baby bed and feeding bottles.
But Leung, who was desperate for a child, strangled Lee with a cord and then sliced open her belly as she lay unconscious. Leung's husband discovered the bloody scene when he arrived home and called police.
Lee survived the assault but her unborn infant, which was 37-weeks at the time of the attack, suffered a brain injury and impaired bodily functions, according to earlier reports.
It died a short time later after an emergency caesarean section at a local hospital.
Psychiatric reports indicated that the defendant had a personality disorder, broadcaster RTHK said.
High Court Judge Darryl Saw said the 10-year sentence took into account Leung's guilty plea to a manslaughter charge and the danger she posed to society.
The court heard that the defendant claimed to have suffered miscarriages in 2003 and, since 2008, pretended to be pregnant by wearing towels tied under her clothes.
Even her husband did not know that Leung's pregnancy was fake until the day of the attack, media reports said.
Leung persuaded a doctor to give her a maternity leave certificate and even put her own name on other women's ultrasound images to show family and friends, according to the reports.