"PRIMETIME LIVE" PRESENTS "A SEPARATE HOPE" -- CHARLES GIBSON REPORTS ON THE INCREDIBLE STRUGGLE TO SEPARATE CONJOINED BABY GIRLS

ABC News' "Primetime Live" Airs Thursday, January 6 at 10:00 p.m., ET

When a sonogram revealed that their twin girls were conjoined at the chest, Kevin and Melissa Buckles suddenly faced daunting decisions and long odds. Conjoined twins are extraordinarily rare-and their chances of survival are slim. "Primetime Live's" Charles Gibson has the dramatic story of how the Buckles made their difficult choice, and cameras chronicle the heroic efforts of doctors from Washington, DC's Children's National Medical Center to separate four-month-old Jade and Erin. For these skilled surgeons, the margin of error was small, and the outcome far from certain. "Primetime Live" airs THURSDAY, JANUARY 6 (10:00-11:00 p.m., ET) on the ABC Television Network.

Kevin Buckles of Stafford, VA, is a gunnery sergeant in the Marines; his wife, Melissa, is a school teacher. They tell Gibson they were shocked but undaunted by their predicament. "Once we saw their faces on the ultrasound, there was no doubt in our mind that, whatever happened, we could make it through," Kevin tells Gibson. The Buckles granted "Primetime Live" remarkable access, allowing cameras to document their trying ordeal-with all of the emotional peaks and valleys-regardless of the outcome.

Gibson and cameras are also inside the operating room during the marathon eight-hour surgery, as doctors do painstaking work to execute their intricate plan and encounter some unexpected roadblocks. Going in, doctors knew the surgery would be precarious. They had expanded the girls' skin with the hope that there would be enough to cover their reconstructed chest walls during surgery. In the o.r., they must deal with a surprising development when they discover the girls have a bridge of tissue connecting hearts that beat in unison. A risky procedure to address this issue has the entire surgical team holding its collective breath.

Even when the surgery is over, the girls' fate is still in doubt. Afterwards, the Buckles share their thoughts about the surprising aftermath and whether they have any regrets about the choices they've made.

DIANE SAWYER, CHRIS CUOMO, CYNTHIA MCFADDEN and JOHN QUINONES are the anchors of "Primetime Live." SHELLEY ROSS is the executive producer.