Republican presidential candidate Rick Santorum is heading back to the campaign trail Monday after a rough weekend. His 3-year-old daughter Bella, who suffers from Trisomy 18 or Edwards syndrome, was hospitalized in Philadelphia for pneumonia on Saturday.

Santorum said his daughter, whose full name is Isabella Maria Santorum, has had a miraculous turnaround at the Children's Hospital of Philadelphia after a very hectic last 36 hours, according to Politico. Her condition led the former Pennsylvania senator to cancel three events, but he said he would attend a scheduled event in Missouri as long as she continues to improve.

Bella and her struggle with Trisomy 18 has become a major symbol of her father's campaign and anti-abortion stance. Santorum has mentioned her in interviews and she has been the focus of a campaign ad.

Trisomy 18 is a genetic disorder in which a person has an extra copy of material from chromosome 18. Unlike Down syndrome, which is also caused by a chromosomal defect (and is also called Trisomy 21), Trisomy 18 is much more life-threatening in early ages, according to the Trisomy 18 Foundation.

Santorum has said Bella specifically has problems with her lungs and has been to the hospital for severe breathing problems before.

Life for the Santorum family has improved dramatically since this afternoon, he told Florida voters in a telephone town hall.

She's got a mask on because she needs help breathing, but she's smiling through it, Santorum said, according to Politico.

At age three, Bella is one of few children with Trisomy 18 to make it past infancy. Most with the chromosomal disorder die before they're born and about half of infants do not survive for more than a week, according to the U.S. National Library of Medicine. On average, one in 10 make it to their first birthday and only 1 percent live to be 10 years old, but they live with severe physical and mental disabilities.

According to the Trisomy 18 Foundation, typical characteristics of the children affected with the disorder include heart defects, kidney problems, clenched hands and delayed growth. Children also usually have a small, strawberry-shaped head, low-set ears, rocker bottom feet (rounded bottoms).

Santorum said he regards his daughter as a miracle. Although doctors said she would likely die of respiratory failure, the candidate recalled during a Thanksgiving Family Forum how he refused to listen to a pediatrician's advice to let go.

I'll do everything to commit to her, and every child like her, Santorum said at the November forum in Des Moines, Iowa, held by conservative Christian groups.