In July 2016, two girls named Erin and Abby Delaney were born in Philadelphia under extremely rare circumstances: they were conjoined twins, joined at the head. Their skulls, and some portions of the brain membranes, were physically fused—a condition so serious that doctors warned from the very beginning that without a risky and complicated surgery, their survival would be in grave jeopardy.

When the girls were only ten months old, medical specialists determined that separation was the only viable option for their long-term well-being. It was understood that the surgery would be unprecedentedly challenging—not only would the surgeons have to separate the bones of the skull, but parts of the brain tissue were also intertwined. The stakes were high: one misstep, even of a millimeter, could lead to death or severe disability. Their parents were fully briefed—there was a real possibility that one of the twins might not survive the procedure.

The surgery itself lasted over ten hours. Surgeons, neurologists, and other experts worked meticulously, planning each detail. Against all odds, the operation was successful: both Erin and Abby survived.

Yet the operation was only the beginning of a long journey. After their separation, Erin and Abby needed extensive rehabilitation. They had to acquire many physical skills that infants usually pick up early on—holding up their heads, sitting upright, crawling or otherwise learning motor control. Their brains had to adapt to their new independent states; the healing process involved years of therapy, effort, patience, and the full support of medical teams, caregivers, and most of all, their family.

Today, Erin and Abby are nine years old. Their growth is somewhat delayed compared to children of the same age—certain developmental milestones took longer. They still require more medical appointments and rehabilitation than many of their peers. But despite all the challenges, they live lives much like other children: they laugh, play, learn, and enjoy the love of family.

One of the sweetest outcomes, their mother says, is that the sisters now can embrace each other. Often, they fall asleep holding one another, and their mother describes this as one of the most precious sights she could ever imagine.

Though their start in life was anything but ordinary, Erin and Abby have made immense progress. Their story is one not only of medical triumph but also of human resilience: of doctors’ courage, parents’ hope, and two young sisters who, against daunting odds, are growing, loving, and living as fully as possible.