The fetus weighed less than two pounds, the coroner said, and would not have been from a viable birth.
Still, police are looking for the woman who carried the fetus, saying she may be in need of medical attention.
The discovery was made early Saturday morning on a porch in the 4900 block of North Marvine Street.
The fetus, an African-American girl who still had her umbilical cord attached, was wrapped in a brown bath towel.
