Raleigh, N.C. — A few years ago, Joanne and Blaine Reese wondered if they could ever have healthy children.

Their first child, Joseph, was diagnosed with spinal muscular atrophy six weeks after he was born in 2006. The genetic disorder causes progressive degeneration and weakness of muscles, including those used in breathing and eating, and is fatal.

Joseph died when he was 5 months old.

The Reeses worried that, if they had another child, it would have a one-in-four chance of carrying the spinal muscular atrophy gene.

The couple went to Carolina Conceptions, a fertility clinic in Raleigh, for in vitro fertilization and a procedure called pre-implantation genetic diagnosis, or PGD.

PGD biopsies a 3-day-old embryo to determine if it carries genetic markers for spinal muscular atrophy or other inherited illnesses, Dr. Grace Couchman said.

"A very tiny, little laser hole is made in the embryo. A single cell is taken out, and those single cells are sent for genetic analysis," Couchman said. "We will be able to find out which of the embryos are actually healthy – the embryos that do not carry the affected genetic disorder."

The Reeses struggled with the decision to use the genetic test.

"How far is too far?" Blaine Reese said, noting that he and his wife consulted their pastor.

"He said, 'You're not asking for a 6-foot-3 boy with blue eyes and blond hair who's going to run the 40 (meters) in four seconds. You're asking for a healthy child,'" he said.

Still, Dr. Jacques Mistrot, a retired cardiac surgeon who teaches bio-ethics through the Catholic Diocese of Raleigh, said the procedure raises questions about the embryos that are found to have a genetic disorder.

"I pray that the day will come with this technology that we'll be able to eliminate the defective gene and not the defective child," Mistrot said. "To get that normal child ... is a wonderful end, but the means have to be examined."

More than 500,000 human embryos are in frozen storage in the U.S. Most are reserved for possible use in future pregnancies, and President Barack Obama last year lifted restrictions on government funding for stem cell research using donated embryos.

Parents decide the fate of all embryos, including those found to have genetic defects.

Using PGD, the Reeses have gotten two healthy children, 2-year-old Haley and 3½-month-old Ross.

"We still have four embryos that we have frozen," Joanne Reese said. "We have not ruled out having more children, but right now, we're pretty happy having two healthy children."