Fresh concerns have been raised about the treatment of inmates at Perth's Bandyup Prison after a woman gave birth alone in her cell, despite calls for help.

The woman, whose age is not being released to protect her privacy, was 36 weeks pregnant when she gave birth last month, alone and without pain relief, after staff were unable to open her cell door.

A spokesman for the West Australian Justice Department described the incident as "extremely rare".

"Pregnant women are medically assessed when received into custody and provided with ongoing pre-natal care and support that are commensurate with health standards in the wider community," the spokesman said.

He said the birth was "unexpected" and the woman gave birth soon after going into labour.

"Staff acted as soon as they could to manage the unexpected birth," he said.

The circumstances of the incident are being reviewed to ensure any necessary improvements to procedures are made.

'This would have been highly traumatic'

The independent Inspector of Custodial Services, Professor Neil Morgan, said the incident raised serious concerns about the treatment of prisoners.

"This was potentially a dangerous situation of course with the birth, something could have happened to the mother or to the child," he said.

"[But] obviously they got in relatively soon after the birth and provided assistance."

He said the incident would have been stressful for all concerned.

"This would have been highly traumatic for the woman herself, but it also would have been traumatic for those staff who wanted to render assistance and were unable to do so in the time they would have liked," he said.

It comes after concerns were raised last week when it was revealed a 20-year-old woman was transported from the prison to a mental health facility while she was naked, bleeding from menstruation, and in severe distress.

'Absolutely outrageous'

Prison advocate Dorothy Goulding was angered by the recent events at the prison.

"This is absolutely outrageous. Things seems to have gone from bad to worse in the prison sector," Dr Goulding said.

"Last year the incident where the young woman who was transported naked whilst menstruating — it's inhumane.

"The whole notion of someone giving birth alone in a cell is just appalling, it's such huge risk for mother and child.

"The dangerous situation of this can't be too strongly emphasized, it could have had dire consequences."

The incident is being reviewed by the Department of Justice.