Most parents would do anything to keep their children safe.
But what can parents do when their child is sick with a deadly disease and requires a bone marrow transplant?
Many in this situation are turning to a controversial procedure in which they choose to have another baby genetically selected from embryos created outside the womb to save the life of their sick child.
The following are several stories of families who made the choice to have a genetically selected baby to save their child's life.
Elisabeth and Michael Hartmann
When Elisabeth Hartmann was 10 years old, she got a baby brother named Michael who literally saved her from death.
Elisabeth was dying of a disease called Fanconi anemia that wasn't letting her body make healthy blood.
"She had very little time left," her father, John, told ABC News.
Elisabeth needed a bone marrow transplant.
"Without treatment she would have died," Elisabeth's mom, Martina, said.
The best option for Elisabeth's survival were stem cells from a close genetic match. And that's what Michael delivered just in time by being born.
"I held the umbilical cord, and [the doctor] milked it into a small, little cup that I was holding, so we could gather this 1 or 2 ounces of precious blood," John said.
But the fact that the blood from Michael's cord was able to save his sister is no accident because Michael was no accident.
He was genetically selected for birth from more than 40 embryos his parents conceived outside the womb using a process called preimplantation genetic diagnosis.
Dr. John Wagner, director of the Division of Hematology-Oncology and Blood and Marrow Transplantation at the University of Minnesota, pioneered the procedure in which a mother is given fertility drugs to make an increased amount of eggs to better the odds of creating an embryo with the right DNA.
Michael was chosen for life over more than 40 other potential siblings because he had what his family needed. The "unchosen" remain in deep freeze or were donated for research.
John Hartmann acknowledges the ethics of choosing which embryo will be born can be debated.
"If you have a dying child, I'm not saying it's OK to do anything, but I think it's OK to use reasonable ethical measures to save your child's life," he said of his family's decision.
But Michael is loved just for being Michael, though his parents know that if they hadn't had Michael, they'd no longer have Elisabeth.
Molly and Adam Nash
John and Lisa Nash knew something was wrong as soon as their daughter, Molly, was born. Before they even held their newborn baby, doctors whisked her away.
Molly had no thumbs, no hip sockets, two holes in her heart and was deaf in one ear.
She was afflicted with the same disease as Elisabeth Hartmann, Fanconi anemia. In Molly's case, the disease would likely lead to bone marrow failure and leukemia. She was not expected to live past the age of 10.
Caring for Molly grew increasingly difficult for her parents. Her disease caused severe digestive problems for Molly, who had trouble eating without vomiting. Doctors had to put a feeding tube in her and perform multiple surgeries on her hands to make them functional.
When Molly was about 3½ years old, her bone marrow started to fail. A bone marrow transplant seemed impossible when a matching donor could not be found.
"We were so brokenhearted, and I really was scared that Molly might not live," Lisa told ABC News' "20/20" in 2001.
Then Wagner told the Nashes of his procedure that could save Molly's life, and the Nashes chose to have a baby that was genetically selected to match Molly's bone marrow.
As the couple struggled to conceive the genetically selected baby through in vitro fertilization, Molly's condition took a turn for the worse.
"She was now starting to require transfusions, her blood counts were such that she was very prone to developing an overwhelming infection at any time ... we were at the very bottom of what we could tolerate," Wagner said on "20/20."
Finally Lisa conceived a son that would be able to help Molly.
"I started screaming and crying. I told Molly she was going to have a brother," she said.
After the baby, Adam, was born, doctors took blood from the placenta. It was given to Molly and ended up saving her life.
Adam was the first child born using this procedure, and many people debated whether the Nashes chose to "play God" when having Adam for the purpose of saving Molly's life.
"God gave us this technology. If God did not want [preimplantation genetic diagnosis] to be available, he would not have allowed the doctors to figure out how to do this," Lisa said.
Anissa and Marissa Ayala
Some parents have tried to conceive a child to help their other sick children without the help of treatments like preimplantation genetic diagnosis.
Abe and Mary Ayala made headlines in the early 1990s when they went public with their intentions to have a third child in the hopes of producing a bone marrow match for their middle child.
The Ayala's daughter, Anissa, had myelogenous leukemia, and a suitable donor could not be found.
Both over the age of 40, Abe reversed the vasectomy he had received nearly two decades earlier and Mary conceived with the hope that their new baby would beat the one in four odds and be match for Anissa.
Abe told The Associated Press that if it weren't for his daughter's illness, "we would have never had another baby this late."
Luckily for the Ayalas, the new baby was a match for Anissa's bone marrow. Fourteen months after she was born, baby Marissa's bone marrow was given to her older sister, saving her life.
Abe and Mary's decision to conceive Marissa solely for the purpose of saving their other daughter's life created ethical debates across the country. After the transplant, the sisters appeared on the June 17, 1991, cover of Time and were the subject of the 1993 TV movie "For the Love of My Child: The Anissa Ayala Story."
Now 35, Anissa recognizes the special bond her parents' decision created between her and Marissa.
"What they did was really, completely just a blessing," she told Newsday. "My sister is the one who will tell you that without me she wouldn't be here, and without her, I wouldn't be here."
Anissa now works for the National Bone Marrow Registry.