The girl's parents are no more and she lives with her 32-year-old brother and an elder sister in Bhopal Vihar in Jaibhimnagar.
The girl had complained of a stomachache on Saturday evening, police said adding that upon visiting the doctor it was revealed that the the girl was seven months pregnant.
On being questioned by her sister the girl disclosed that her brother had raped her. The elder sister then lodged a case against her brother in the Bhavanagar station, police said.
The brother's wife had separated from him four years ago and the victim was married twice but both times was dumped by her in-laws.