A South Carolina mother killed her four-day-old son by putting him in the refrigerator for three hours, authorities said.

Angela Blackwell is charged with homicide by child abuse.

During a brief court appearance on Tuesday, the judge explained that because of the severity of the charges no bond could be set at the initial hearing, in accordance with state law.

She only nodded and shook her head, leaving the small courtroom after a few minutes without a sound.

Blackwell, 27, was arrested on Monday, nearly six months after her son died. Investigators said they have spent that time taking statements and getting forensic tests done on the baby.

A post-mortem showed that the boy, William David Blackwell, died from hypothermia with asphyxiation from being placed in the cold, according to Chester County Coroner Terry Tinker. First-responders tried to revive him on February 27, but he was pronounced dead at a hospital.

The baby's grandfather, Billy Lewis, told reporters gathered at his home before his bond hearing that Blackwell was sad around the time of her baby's birth, but appeared to be cheered up after her son was born.

"She didn't do it. We don't know who did it, but she didn't do it," said Mr Lewis, who added there were other people in the home.

Authorities also have not talked about why Blackwell may have placed her son in the refrigerator. Blackwell's next court appearance is November 10.

Neighbours said the Blackwells were nearly evicted from their home recently because the yard was a mess. Children's toys are still strewn in the backyard, and an old rusted car without an engine and a white hearse that has seen better days remain in the front yard. While everyone knew about their yard, no one seemed to really know them, neighbour Dot Corley said on Tuesday.

"She didn't say anything to anybody that I know of," Ms Corley said.

According to an online obituary for her infant son, Blackwell has another child. A Facebook profile that appears to belong to Blackwell shows her posing with a toddler and a newborn in photos posted the day after William's birth.

The boy's father, who is not charged in connection to his death, has a lengthy arrest record. Jeffery Paul Lewis, 35, has theft convictions in South Carolina dating back to 2005 and served more than two years in prison after a probation violation, Corrections Department spokeswoman Stephanie Givens said.