When Maggie and Dom Altobelli went for a routine ultrasound during pregnancy, they expected to see their babies developing normally. Instead, the scan revealed something extraordinarily rare: they were expecting conjoined twins.

The girls, later named Addison “Addy” and Lilianna “Lily” Altobelli, were joined at the chest and abdomen—a condition known as thoraco-omphalopagus conjoined twins. Their story would eventually become one of the most remarkable separation cases treated at Children’s Hospital of Philadelphia (CHOP).

A rare and complex connection

Conjoined twins occur in approximately one in every 50,000 births, making each case exceptionally rare. In Addy and Lily’s case, the girls shared portions of their chest and abdominal walls, their diaphragm and a liver, while their hearts were separate and healthy. Doctors determined that the shared liver was large enough to be divided between them, making surgical separation a realistic possibility.

The diagnosis came at around 20 weeks of pregnancy. Maggie and Dom were referred to CHOP, where a multidisciplinary team began months of detailed examinations and planning.

The objective was not simply to separate the girls. Doctors needed to understand precisely how their organs and blood vessels were connected and determine whether both babies could survive independently after surgery.

Months of preparation before the operation

Because separating the twins would leave large areas of exposed chest and abdominal wall, surgeons needed to make sure each girl would have enough skin to cover her reconstructed body.

CHOP plastic surgeon David W. Low, MD, placed tissue expanders in the girls. These devices functioned much like small balloons: medical teams gradually filled them with fluid over time, stretching the children’s skin and creating additional tissue for use during reconstruction.

At the same time, the medical team conducted extensive imaging studies and repeatedly reviewed the surgical plan.

The complexity was so great that doctors even created three-dimensional models of the twins’ anatomy. These models helped the surgical team visualize how the girls were connected and rehearse the sequence of the operation before entering the operating room.

More than two dozen specialists were ultimately involved, including pediatric surgeons, cardiothoracic surgeons, plastic surgeons, anesthesiologists and radiologists.

The 10-hour operation

Addy and Lily were born at CHOP on November 18, 2020. They then spent almost a year receiving intensive medical care and preparing for the separation.

Finally, on October 13, 2021, at approximately 10 months of age, the sisters entered the operating room for the procedure that would change their lives.

The surgery lasted 10 hours.

Led by pediatric and fetal surgeon Holly Hedrick, MD, the team carefully divided the structures connecting the twins. At 2:38 p.m., Addy and Lily were officially separated for the first time in their lives.

But the procedure was far from finished.

Once the girls were separated, the medical team divided into two groups and simultaneously worked to reconstruct each child’s chest and abdominal wall. Surgeons used layers of surgical mesh and the additional skin created by the tissue expanders to protect and stabilize their bodies.

The moment their parents had dreamed about

For Maggie and Dom, the most emotional moment came after the surgery.

For the first time since their daughters had developed in the womb, Addy and Lily were lying in separate cribs, with their own bodies and their own space.

Their father described seeing them as separate children as an incredible and deeply emotional experience. After months of uncertainty and preparation, the family finally knew that both girls had made it through the operation.

The road to recovery, however, was still long.

The twins spent approximately seven weeks in CHOP’s Pediatric Intensive Care Unit following the separation. Their progress was closely monitored before they were eventually transferred to Lurie Children’s Hospital in Chicago for continued care closer to home.

A new life as two sisters

In December 2021, Addy and Lily finally returned to Chicago. They had spent more than a year receiving care away from home, and their return marked a new chapter for the family.

CHOP later reported that the girls continued to thrive. By 2024, three years after their separation, they were described as active young children, continuing to grow and reach new milestones. Their medical journey was gradually becoming less about surviving a complex operation and more about simply being children.

Their story also inspired the creation of the Addy and Lily Fund for Transformational Surgical Care, established to support advances in personalized pediatric surgery and help other families facing similarly complex medical challenges.

Today, Addy and Lily’s journey stands as a powerful example of what can happen when advanced imaging, meticulous surgical planning and the collaboration of dozens of medical specialists come together.

They were once connected by anatomy that doctors had to understand down to the smallest detail. After a painstaking 10-hour operation, they emerged as two separate children—two sisters given the opportunity to grow, play and experience life independently.

Their story is not simply about a rare medical condition. It is about precision, perseverance and the extraordinary possibilities of modern pediatric medicine.

Sources

• Children’s Hospital of Philadelphia (CHOP) — The Story of Addy and Lily: Birth and Separation of Conjoined Twins
• Children’s Hospital of Philadelphia (CHOP) — CHOP Surgeons Separate Twin Girls Joined at the Chest and Abdomen
• Children’s Hospital of Philadelphia (CHOP) — CHOP Announces Dollar-for-Dollar Matching Gift Campaign
• Children’s Hospital of Philadelphia (CHOP) — Conjoined Twins Separation Story
• Children’s Hospital of Philadelphia (CHOP) — Follow-up report on Addy and Lily, 2024.