Family members say that the child died on Thursday.
Another woman and her two children were also struck by the vehicle. They survived.
Firefighters and paramedics worked to keep Brown alive as long as they possibly could to take her baby. "Once we then triaged the rest of our patients, we decided that she was going to be the priority and we were going to save her to save her child," said Tony Behland, Engine Company 95.
Brown had only a faint pulse and very labored breathing.
"I put a tube down into her lungs and... I secured her air way and we started doing CPR on her," said Captain Jill Gariti, Ambulance 15.
Paramedics continued CPR all the way to the hospital. They managed to keep her alive until they got to the hospital. Brown's injuries, though, were too severe and she died shortly after arriving at the hospital. Doctors delivered her son by C-section.
"Obviously there are challenges when a baby is premature. But these challenges are exacerbated by the fact that there were a number of injuries the baby sustained in the accident," said Marcel Bright, Stroger Hospital spokesperson.
The hospital has not released a statement on the baby's death.
The driver of the van that led to the accident, 39-year-old James Cox, faces several traffic citations, including running a red light and driving without insurance and on a suspended license.
The Secretary Of State's Office says Cox has a long history of traffic violations and hasn't had a valid license since 2002.