Breathless Bride Races Against Cystic Fibrosis Doctors said Kirstie Mills Tancock may not make it to the alter without a new set of lungs. The 21-year-old from Devon in the United Kingdom has known since birth that she was living on borrowed time -- she was born with cystic fibrosis. And just days before her dream wedding last year, her lungs filled with a life-threatening infection. "I have spent every moment living like it was my last," said Tancock, who, until her health spiraled downward, was a fit athlete and worked as a pole dance instructor. "I take life as it comes," she said. You never know what's going to happen. Just because you know your life will end doesn't mean you have control. Television cameras followed Tancock for four months last year as she simultaneously planned her wedding and waited for a lung transplant. "Breathless Bride: Dying to Live" will air on TLC on Feb. 29 at 10 p.m. In the documentary, Tancock was confined to a wheelchair and hooked up around the clock to an IV for strong pain medication and antibiotics. Just days after her June 16 wedding, she was air lifted by medevac to a London hospital for a lifesaving double lung transplant. "Kirstie is a complete fighter," said her husband Stuart Tancock, 27, and a sports store manager, in the documentary. You can't put her down ? She'll fight for anything. Tancock has known since a young age that her life was expected to be short. She was born with cystic fibrosis, an inherited chronic disease that affects the lungs and digestive system. About 30,000 children and adults in the United States have the disease. About 1,000 new cases are diagnosed each year in the U.S., and about one in three people with the disease will die waiting for a lung transplant. A defective gene and its protein product cause the body to produce unusually thick, sticky mucus that clogs the lungs and leads to life-threatening infections, according to the Cystic Fibrosis Foundation. The disease also obstructs the pancreas and stops natural enzymes from helping the body break down and absorb food. Only a half century ago, few children with CF lived to attend elementary school. Today, medical advances have extended the average life span of someone with CF well into their 30s and 40s. According to the CF Patient Registry, nearly 1,600 people with the disease have received lung transplants since 1991. As many as 90 percent are alive one year after transplantation and half are still living after five years. As Tancock's story begins, the clock is ticking. Her incessant cough disrupts her every activity as she gasps for air, even as she rides as a passenger in a car for some pre-wedding shopping. At night she wears a mask so that oxygen can be forced into her lungs while she sleeps. Her lung function dropped to 16 percent of a normal person's, according to Dr. Nick Withers, who treated Tancock and was featured on "Dying to Breathe." CF patients are referred for transplantation when lung function drops to 33 percent. "She is living on a knife edge," he says. Anything can tip her over. Tancock is optimistic, but also a "realist." "I didn't expect to be here at 21," she says, with her oxygen tank in tow. But that's not the worst thing -- I'd love to have working lungs ? CF has made me who I am, but I'd trade it in a heartbeat. Cystic Fibrosis: 'It's Like She's Suffocating' Tancock's then fiance knew what he was getting into when he proposed to her. "In life, you don't know who you will fall in love with," he says. But I would rather something short, and be as happy as we can be, than a lifetime of just going through the motions. But it's still difficult to watch her pained breathing. "It's like she's suffocating, drowning," says Stuart Tancock. You don't want to see anyone suffer, especially someone you love. If I could take one day and be her -- so she could get a day off. Two days before the wedding, Tancock awakes and her lips and ears are blue -- her face is ashen gray. She has a temperature, which means infection. "She can't breathe," says Stuart Tancock. This has never happened before. Her doctors encourage Tancock to have her wedding in the hospital, but she refuses. Against their advice, the wedding goes on and three CF nurses accompany her in case of an emergency. Tancock is hanging by a thread. Stuart Tancock wipes away his tears as he pays tribute to his courageous bride. A silver satin bag made by her aunt discretely hides her oxygen tank. "She's got drive and determination like no one else in the world," he says. That's why I'm marrying her. Eight days after the wedding -- and after three months on the transplant list -- the couple gets a call that finally lungs are available for transplant. But after Tancock is rushed to a specialized hospital in London, doctors discover the organs are too big for her body. Doctors say she needs a miracle to live. Two weeks later, her miracle arrives; another set of lungs become available and they are a match. Tancock endures a four-and-a-half hour surgery. "I was just hours from death," she told ABC News, recalling the "intense and traumatic" pain. At one point, she even tried to get her family to shut off the machines that had been keeping alive. "I was in and out of sedation and very sick," she said. From time to time I came around and tried to communicate with people. I had given up, enough is enough, I had drawn a line. Now, Tancock said she is healthy, "Fitter than I have ever been" -- though her recovery was long and difficult. "I couldn't hold my head up," she said. A tracheotomy had wasted away her vocal chords and she had to relearn to talk. She will have to take anti-rejection medication for the rest of her life and needs antibiotics because her immune system is suppressed. Today, she writes a blog, 2nd Chance at Life, and volunteers with organ transplantation and cystic fibrosis organizations in her native Britain. She is also training for a 180-mile bike ride in September for charity. She agreed to participate in the documentary because, she said, "People don't get to see what living with CF is like." She hopes "Dying to Breathe" will raise awareness. Tancock said she is not religious, but draws strength from a sense that there is some sort of afterlife. An experience while she was near death suggests she may be right. "My friend passed away when I was 10, and it was her birthday that day," when Tancock almost died, she said. She was 16 and my first connection to CF. Debby died within weeks of receiving her lung transplant. And Tancock said her friend appeared as an apparition, just as she was ready to give up. It was her, telling me to keep holding on. The battle isn't over, even though her new lungs may give Tancock another decade or two of life. CF will continue to slowly ravage her body. Somehow, she still manages to stay positive. "I am lucky even if I get just one more day of life out of this," she said. At the same, there can be complications -- this is not a cure. I could reject the lungs tomorrow. Nothing is guaranteed, but I try my best and do what I can. She added, "Today, I can be who I want to be."