A woman three months pregnant was struck by a runaway taxi near Union Square last night after the driver left the vehicle to chase down a fare-beater, cops and witnesses said.

Sam Kizy hopped out of his yellow cab at around 6:25 p.m. It was still in gear.

“I heard people screaming, and I turned around as it hit me from behind,” said victim Anna Wasilewski. Neither Wasilewski nor her child was harmed.