With an estimated five weeks left to go before their daughter dies of cystic fibrosis, parents of Sarah Murnaghan are determined to fight a system they believe is unjustly keeping their 10-year-old girl from receiving the donated lungs that could save her life.

Pediatric lungs are uncommon and the Murnaghan family thought Sarah would have a chance at a transplant when she made a list of adults, Fox News reports.

All that changed, however, when the family discovered a national organ rule standing in their way.

The family were told that the dying girl is two years too young to be placed on the adult list, regardless of how dire her circumstance. And while Sarah is a top priority on the pediatric list, doctors warn there are far fewer pediatric donors, meaning adults in her region with her blood type will be offered the lungs first, despite having less severe conditions.

For example, the United Network for Organ Sharing (UNOS) reports there were only 10 transplants in Sarah’s age group in 2012, whereas there were more than 1,700 adults during that same time period.

“I was shocked,” the mother Janet told CNN about the discovery, especially considering the family has been waiting for 18 months, during which time Janet said she “did her research.”

Dr. Stuart Sweet of St. Louis Children’s Hospital is a board member at the UNOS and helped write the current system regarding pediatric transplants. And though he admits that Sarah’s story “tugs at the hearts,” he argues that should the system be changed to favor those like Sarah, “there’s another patient, very likely an adolescent, who gets a disadvantage.”

Janet, however, denies that what they’re looking for is preferential treatment, but rather “equal treatment,” telling the Associated Press that they “want it be a triage system like they do for everyone else where the sickest patient goes first and ones with the ability to wait, wait.”

And while she recognizes that fewer children are dying while awaiting transplants, the number, she says, represents a higher proportion relative to the number on the waiting list.

“They’re allowing children to die at a far greater rate than adults,” she said. “The system is set up to prefer adults and the data supports that.”