0756 GMT October 14, 2019
The woman, identified only as Amy, had told staff two hours earlier that she believed she might be in labor, BBC reported.
There were no complications at the birth.
The March incident was in a maximum security cell in Western Australia's only women's prison. A review found the event had exposed a series of failures.
One of them was that no alarm had been raised.
Amy had been sent to Bandyup Women's Prison in the late stages of pregnancy after failing to meet the conditions of her bail, Australian media reported.
At 17:30 local time (09:30 GMT) on March 11, she called from her cell to inform staff that she was distressed and possibly in labor.
After being taken for a health assessment, she reported abdominal pain but did not say she was in labor. Nurses were not informed of her earlier statement.
She was given paracetamol and returned to her cell, but became "audibly distressed" about 18:30 and began pleading for help.
Amy gave birth about 19:40. Nursing staff had arrived about five minutes earlier, but could not gain access to her cell because the only staff member with keys was not nearby.
The nurses had been forced to communicate with her through a hatch in the door, said the review by the state Inspector of Custodial Services Neil Morgan.
Amy and her baby were taken to hospital later that night.
Professor Morgan said he undertook the review "to understand how such distressing, degrading and high risk set of events could have occurred in a 21st Century Australian prison."
His key findings were that: