Darla Napora, 32, was killed inside their home on Reina Del Mar Avenue.
Pacifica police arrived at the home after getting a 911 call from the victim's husband.
"When they arrived, they found the victim laying in her own front living room; she was not breathing, unresponsive and had major trauma to her upper body," Pacifica Police Capt. Dave Bertini said. "The husband stated that when he got home, at about noon, he found his wife with their pit bull hovering over her."
Darla and Greg Napora owned two pit bulls, a spayed 6-year-old and an unneutered 2-year-old. The unneutered pit bull is believed to be responsible for mauling and killing Darla.
Police ultimately shot and killed the dog after it escaped from the backyard as officers were conducting their investigation.
"The last thing we wanted to happen was for the dog to get out and start attacking bystanders or be loose in the neighborhood," Bertini said. "So as soon as the dog got out of the backyard, the decision was immediately made to put that dog down and that's why the dog was shot three times by two officers on scene."
Police say Darla was pregnant, although they do not know how far along she was.
Neighbors are saddened. They say the dogs appeared nice and normal and never noticed anything unusual about the dogs.
A necropsy is scheduled for Friday.
"Eventually we're going to find out if there's anything physically or medically wrong with the dog that may have caused this attack," Bertini said. "We have already done an extensive interview with the husband and there are follow up questions that we may ask in the future."
Police do not believe the other pit bull had anything to do with the attack but as a precaution it is being held at the Peninsula Humane Society.