Formerly Conjoined Sisters Celebrate 1st Birthday Before Leaving Hospital

— -- A pair of formerly conjoined sisters celebrated their first birthday this week before finally getting to leave the hospital for the first time.

Scarlett and Ximena Hernandez-Torres were born connected at the waist, sharing a colon and bladder -- a 1 in 50 million chance -- according to the Driscoll Children's Hospital. Last month, they underwent a marathon surgery to separate them. The pair were born with a third sister as a set of triplets last May.

The plan for the separation surgery included high-tech medical devices. Doctors used a special scanner called a "spy camera" during the surgery to understand the complicated blood flow between the girls and help them stay healthy during the long ordeal. Additionally, doctors used a 3-D model from a specialized MRI, designed to help them map out the surgery.

Just a month after the surgery, the girls were able to celebrate their first birthday just one day before they were declared healthy enough to be able to leave the hospital for the first time, officials from the Driscoll Children's Hospital told ABC News. They joined their sister and older brother at a nearby Ronald McDonald House as they continue to recover from their surgery.

The girls' mother, Silvia Hernandez, told ABC News in an earlier interview that she can already see a difference in her daughters' personalities.

"Scarlett likes to dance, sing and she smiles a lot," she said. "Ximena is most of the time sleeping but she smiles a lot."

The girls were born as triplets with a third sister, who was not conjoined. Hernandez said in an earlier interview that she was concerned about the girls' health and mobility after the surgery.

"I do have to believe in God's will, that everything will be fine," she said. "And he will be there in the day of the surgery and he will make a miracle with them."