It happened Wednesday night near 59th and Racine. Witnesses say the dog attacked the pregnant woman and her boyfriend as they were leaving a home.
A police officer arrived on the scene moments after the attack. He shot and killed the dog after the victims managed to break free and get to safety.
""They shot the dog once and he kept trying to attack the officer. So they opened fire again, nine, 10 more times. It took that many shots to put that dog down," said witness Marlo Weathers.
Police are trying to find the owner of the pit bull.
The female victim is hospitalized in fair condition. The man was treated for a bite to his leg.