A man made a pact with his wife to have sex with his teenage stepdaughter because the couple desperately wanted another child.
The trio wrote the agreement down in a notebook and the woman - the girl's mother - offered her 15-year-old daughter advice on the best sexual positions to achieve their goal.
Today the man, 35, was sentenced to eight years in jail, while the girl's 39-year-old mother received a six month jail term, to be followed by three years probation.
Both had pleaded guilty to one charge each of maintaining a sexual relationship with a child.
The Brisbane District Court was told the man made the pact with his wife in May 2006 to get the teenager pregnant because they wanted another child.
Prosecutor Catherine Semmler told the court the couple already had two sons, but that both had been born with a congenital disorder.
It was the fear of passing on this disorder that prompted them to manipulate the girl into participating in their bizarre scheme, she said.
The court was told the girl, then 15, initially used a syringe to try to artificially inseminate herself with her stepfather's semen.
When this was unsuccessful, the man started having sex with the girl up to three times a day at their home at Russell Island, south-east of Brisbane, between April and August 2006.
However, Ms Semmler said, the man had already been sexually abusing his stepdaughter since she was 12.
The court was told the teenager succumbed to his advances until the day after her 16th birthday, when she filed a complaint with police.
The court heard that when the man was arrested he referred to a written pact, asking police: "Did you not see the f***ing contract?"
Handing down sentence, Judge Michael Forde said: "This bizarre agreement could only be described as dispicable conduct by both of you."
He told the woman:"You have completely breached the trust that a daughter has in a mother."
Even defence lawyer James Crowley, who represented the man, said the couple's actions were "disgusting and dispicable".
However he said his client was "very remorseful".
