TIAHLEIGH Palmer may have been pregnant at the time of her death, the Beenleigh Magistrates Court has heard.
On Wednesday the court heard the 12-year-old's foster brother, 19-year-old Trent Jordan Thorburn, was worried he had impregnated her.
It is alleged he confessed to his cousin in a message on Facebook that he had sex with Tiahleigh, and was concerned she was pregnant.
He was denied bail with the police prosecutor saying "if he is released on bail he will hinder and interfere with the murder investigation".
Prosecutors told the court Thorburn had "taken advantage of her as her big brother, and as a result her young life has been taken".
On Tuesday his father, 56-year-old Richard Neville Thorburn from Chambers Flat, was charged with her murder.
He was due to appear in court on Wednesday morning, but his lawyer revealed he was in an induced coma in the Princess Alexandra Hospital after collapsing on Tuesday afternoon.
Tiahleigh's foster mother, Julene Thorburn, 54, and oldest foster brother, Josh Thorburn, 20, were both charged with one count each of perjury and attempting to pervert the course of justice.
Both Julene and Joshua Thorburn are due to appear in the Beenleigh Magistrates Court on October 10.
On Tuesday Detective Inspector Damien Hansen addressed the media saying he expected Julene, Trent and Joshua Thorburn to be key witnesses.
The 12-year-old Marsden schoolgirl's body was found on the banks of the Pimpama River in November last year.