An Illinois driver remains at large after fatally striking a pregnant woman while she was crossing the street, according to the Waukegan Police Department.

       At approximately 9:34 p.m. on Sunday, officials responded to a report of a "vehicle crash with injuries, involving a pedestrian," police said in a press release obtained by ABC News.

       Once at the scene, police and fire officials found the pedestrian, identified as 36-year-old Michelle Heidbrick, with "critical injuries," authorities said.

       The driver of the vehicle that struck Heidbrick "fled the scene prior to the arrival" of police, according to officials.

       Heidbrick was transported to a local hospital where she was "pronounced dead in the emergency room," police noted.

       Preliminary autopsy results indicate that Heidbrick "died from blunt force injuries as a result of the incident," officials said.

       Heidbrick's sister told ABC Chicago station WLS she was "sweet" and "wouldn't hurt a fly." She told WLS that Heidbrick leaves behind a teenage son.

       Police confirmed Heidbrick was in the second trimester of pregnancy.

       "She had called me last week and was excited. She's like 'Nicole, I felt the baby kick for the first time,'" Nicole Heidbrick told WLS.

       She told WLS the family is demanding that "somebody come forward."

       The incident "remains under investigation" by police's major crash unit, officials said.