The developmentally and physically disabled woman was taken to a hospital last week after developing medical complications from a pregnancy. The woman lives at the Central Wisconsin Center for the Developmentally Disabled in Madison.
Police spokeswoman Laura Walker says investigators are trying to figure out who had access to the woman and put together a timeline.
She declined to discuss the woman's condition.
Most of the 350 residents of the center can't walk, bathe, dress or feed themselves.
Jim Malone is a spokesman for the Department of Health and Family Services, which runs the center. He says the average mental ability of most of the residents there is equivalent to a one-year-old's.
He says DHFS is conducting its own investigation but declined to elaborate.