NEW ORLEANS – Rocking your baby to sleep in a mechanical swing may trigger a deadly attack on the child by the family dog, a coroner warns.

At least two such deaths have been documented in Maryland over a four-year period, Dr. Albert Y. Chu of the state’s medical examiner’s office said Wednesday at a meeting in New Orleans of the American Academy of Forensic Sciences.

The back-and-forth motion may activate the dog’s instinct to chase prey, he said.

“Think about dogs chasing cars or tennis balls. They can’t control their behavior – they just go,” he said.

In 2003, a 2-week-old boy was dragged from his swing and killed by the family’s pit bull in Baltimore after the baby’s mother left him to answer the front door. In Edgemere, Md., in 1999, a 3-month-old boy was mauled to death as his parents slept in another room.

An Associated Press check of online news archives found at least one more death – that of an 18-day-old girl in Tampa, Fla., in 2000 after her mother left the room to warm a bottle for her – and at least two nonfatal attacks around the country in the past few years.

In one of those cases, in Summerville, S.C., in 2003, the dog lunged for the baby and bit her in front of the child’s mother.

In 2000, Sabrina Williamson of Peru, Ind., had gone to the store while her husband napped in another room, about six feet away from 9-week-old Alex. She walked back in and found her husband wrestling their pit bull off the baby. They had had the dog eight years, since Alex’s brother was 4.

“I think it could be a key factor. Our dog had never been mean towards a child before,” she said in a telephone interview.

The baby’s face was bitten and bloody, and his collarbone was broken and protruding from his shoulder, police said.

Dr. Marianne DiPadua of University Foggia in Italy said she is not convinced that the rocking movement sets off the dog. “It’s true movement can trigger an attack,” she said. But she noted that dogs also have attacked babies in cribs or beds.

Dr. Jane Sanders, a radiologist and a board member of the humane society in Jackson, Miss., said she planned to pass on the information to the shelter’s director. Most dog attacks are by pets that have never been aggressive, she said.

Catherine Mills, a Marshall, N.C., dog trainer with 25 years of experience, and John C. Wright, an animal behaviorist at Mercer University, said pets should be conditioned to ignore baby swings before a baby is put into one.

“Put the swing up, leave it on without a baby in it until the dog or cat totally ignores it,” Mills said.