Hivon, 42, has been junior public health minister for a month or so since the PQ's election victory in September.
She is not vacating her seat in the Joliette riding north of Montreal she has represented since 2008.
Hivon told a news conference her doctors said she is at risk for health problems and that she needs to slow down.
"Of course, I want to do everything in my power to have a successful pregnancy, so that is what is governing me right now," said Hivon, who has a four-year-old adopted daughter.
"I think this has to take precedence."
Hivon said she has enjoyed her brief spell in cabinet and that it was a surprise when she found out she was pregnant.
She is still hoping for a long political career.
"I will come back in whatever circumstances....I will have challenges," Hivon added.