The baby's mother was also injured while trying to wrestle the knife away from the maid after she heard her daughter screaming late Tuesday night, the report said.
The newspaper carried a photo of the baby showing her with a long gash running across her chin from one side of her jaw to the other. Doctors used 130 stitches to close her wounds, it said.
Police arrested Zhang Xuexia, 47, who was said to be angry because she believed the family was planning to fire her.
Many Shanghai families employ domestic helpers from the countryside, and relations can often be tense, especially around the time of the Lunar New Year, the country's biggest holiday.
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