A pair of North Carolina sisters who were once joined at the head are home and thriving over a year and a half after undergoing an 11-hour separation surgery, which was the culmination of a months-long effort. Abby and Erin Delaney, who were diagnosed as craniopagus conjoined twins in utero, shared brain tissue, and the blood vessel responsible for carrying blood from the brain to the heart, which complicated the separation surgery.

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“I think they’re doing a lot better than we expected,” Dr. Gregory Heuer, the girls’ neurosurgeon at Children’s Hospital of Philadelphia, told Philly.com. “They may have delays, but the separation process resets the developmental clock. We’re not sure how well they’re going to do ultimately, but that’s a good thing. When we don’t have answers, that makes us feel good to some extent, because it tells us the door is wide open.

The girls had undergone several procedures before the separation, including one to implant an external distraction device. (Children's Hospital of Philadelphia)

According to CHOP, craniopagus conjoined twins occur about six in every 10 million births. And while the hospital has separated 24 pairs of conjoined twins, the girls’ other surgeon, Dr. Jesse Taylor, said at 10-months-old Abby and Erin were “the earliest separations of craniopagus conjoined twins every recorded.”

Months before the girls’ surgeons at CHOP were prepared to officially separate them, the girls had undergone a primary surgery to set up an external distraction device, which gradually pushed the twins apart by one or two millimeters per day. According to CHOP, they then underwent several additional surgeries including a procedure to implant tissue expanders to slowly stretch the skin.

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The surgeons detailed their approach in a Jan. 24 report published in the New England Journal of Medicine, which culminated in the 11-hour surgery involving 30 medical professionals.

The girls face an additional surgery in their future for an implant to repair the opening in their skulls created by the separation procedure. (Children's Hospital of Philadelphia)

The pair were officially separated on June 6, 2017, and while Abby suffered more blood loss and received less of the sagittal sinus, the surgery was a success. The girls were cared for in the intensive care unit and then spent two months in inpatient rehabilitation. Erin was discharged in October 2017, with Abby joining the family one month later. The entire family headed back home to North Carolina before Thanksgiving 2017, where they have been “exceeding all expectations.”

The now toddler-aged sisters will continue to be monitored by their surgical team throughout their childhood, and at some point, they will need an implant to cover the openings in their skulls created during the separation surgery.

The twins, now over 2 years old and pictured here with their surgeons and parents, have started babbling and are involved in physical, developmental and speech therapies. (Children's Hospital of Philadelphia)

Heather Delaney, the girls’ mom, said that Erin has started crawling and that Abby manages to get where she needs to go, typically by rolling. The girls are babbling, and have started to say ‘Mama’ and ‘Dada.’

One difficulty that Heather noted to Philly.com, is that neither of the toddlers is willing to transition to eating solid foods, but they are both on track for growth. Heather said they are both enrolled in physical, developmental and speech therapies.

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“After this long and complicated surgery, these little girls are recovering, developing and growing,” Taylor told CHOP. “We are honored to have helped make this happen.”