QUINCY, Mass. -- Police in Quincy were investigating the slaying of a 9-year-old girl, allegedly at the hands of her pregnant mother, who is hospitalized after also allegedly stabbing her unborn child to death.

Officers were called to the two-family home at 20 Woodbine St. about 10:30 p.m. Thursday to investigate the slaying of the Wollaston girl, identified as Xue Wen. The girl's 14-year-old sister also apparently escaped a strangulation attempt. Police said they were investigating whether the slain girl was also poisoned.

The mother, identified as Fang Chi-Xue, 38, was 7 1/2-months pregnant. She was taken to Boston Medical Center to be treated for self-inflicted stab wounds, police said. Authorities said she will face murder charges when her medical condition improves.

The 14-year-old is staying with relatives. The attacks were believed to have followed an apparent domestic violence argument, police said.

The District Attorney's office said it believes the girl's father called 911.