A male prison officer at Bandyup Prison has been suspended after an inmate became pregnant.
It is understood the guard denies any wrong-doing.
The man was suspended after a 31-year old prisoner, who is serving a four-year sentence for drugs offences, was found to be pregnant several months ago.
The woman has had no known contact with men other than staff at the jail since starting her sentence.
The guard is being investigated for "serious misconduct", although in Western Australia it is not illegal for a prison guard to have consensual sex with a prisoner.
Among corrections officers the case is being referred to as "Bandyup's immaculate conception".
On Saturday morning the Department of Corrective Services released a statement saying that the officer had been suspended as a precautionary measure.
"This does not necessitate that the officer is guilty of any wrong-doing," the statement said.
"The allegation is highly complex and sensitive for the parties concerned.
"The allegation is uncommon and taken very seriously by the Department and the investigation is expected to take at least five months."
The case has also been referred to the Crime and Corruption Commission.
The Prison Officers' Union said the suspended guard was entitled to a full and fair hearing.
"Our member has strenuously denied these allegations," said union state secretary John Welch.
"Once the full nature of the allegations have been put to the officer in question, he will be given the chance to respond and set out his defence.
"This is clearly a very serious allegation and should any prison officer be found guilty in a situation such as this, there would be little support for that person from our members," said Mr Welch.
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