The pregnancy of the 14-year-old girl came to light recently when she met with a road accident and had to be admitted to hospital, police said.
The girl, her parents and younger sister lived on a footpath in the Wagle Estate locality of the city and collected and sold scrap material to earn a livelihood.
On January 6, the girl was knocked down by a vehicle on the road. She suffered injuries in the mishap and was rushed to a hospital in Mulund.
Later, as the girl complained of severe stomachache, she was shifted to Sion Hospital where on Monday the doctors conducted sonography which revealed that she was one-month pregnant, he said.
The doctors took the girl into confidence and probed further when it was revealed that she was allegedly raped by a youth, Mehboob Sayeed (23), who used to target her at the Indira Nagar footpath, police said.
Subsequently, the youth, who did did petty jobs like electrical wiring, was arrested yesterday and booked under section 376 (rape) of the IPC and sections 4, 8 and 12 of the Protection of Children from Sexual Offences (POCSO) Act 2012, police added.