Two thugs mugged a pregnant woman in the lobby of a Midtown building and ran off with her wedding band and engagement ring, police said yesterday.

Surveillance video of the Aug. 19 attack shows the robbers accosting the woman, who is eight-months pregnant, and pinning her against a wall in the vestibule of the building at 37 West 57th St. One of the bandits was brandishing a gun.

The 32-year-old woman had been waiting for her husband to pick her up after her appointment at a beauty salon in the building.