The state cannot intervene until the birth of the child but it wants to speak with the woman to offer counselling and support services.
The woman, in her early 20s and said to be addicted to heroin and speed, has advertised her services on an erotic website, saying she needs money after being abandoned by her partner.
The first-time mother describes herself as a "damsel in distress" who had retired from prostitution but returned after she was "left high and dry by her once very supportive partner of years."
She said it "would be just near impossible or silly to find any type of employment or a employer that would employ someone for a few weeks . . . so I have decided to resume working."
She is marketing herself to men with a "pregnancy fetish."
An acquaintance of the woman said the mother-to-be was "endangering her child" with her drug use.
The woman hung up the phone when contacted by The Courier-Mail.
The newspaper had alerted the Department of Child Safety, which is trying to locate the woman.
"In cases such as this, the department will undertake an investigation, which would include a determination of whether the child is at risk of harm or neglect after it has been born," a spokeswoman said.
The department said newborns had been taken from their mothers after birth but only on "rare" occasions.
Medical experts say unborn babies are in danger of premature birth and serious health risks from sexually transmitted diseases and drug effects.
It is commonly agreed that illegal drugs can be harmful to a fetus and should be avoided during pregnancy. Babies born to heroin-addicted mothers go through withdrawal after birth.
But the department is legally unable to intervene until the child is born.
"However, once the baby is born, the department can and sometimes does remove children at birth where an unacceptable risk of harm and neglect has been identified," the spokeswoman said.
Sex workers usually stop working before or within a few months of pregnancy.