CLEVELAND – Doctors began the first in a series of high-risk surgeries Wednesday to separate 3-year-old twin girls joined at the head.

Doctors hope to separate Tatiana and Anastasia Dogaru, who were born in Italy but are of Romanian descent, through several surgeries in about six months. Without separation, the twins risk dying in early childhood.

The initial surgery lasted all day and didn’t end until early evening. The girls were under close observation in a pediatric intensive care unit. An update on their condition was not expected until Thursday, said Janice Guhl, spokeswoman for University Hospitals’ Rainbow Babies & Children’s Hospital.

Surgeons had said they would begin at the girls’ scalps and slowly make a wedge where the twins’ skulls are joined. They planned to remove a rectangular bone flap and reinsert it at the end of the surgery.

The procedure will give neurosurgeons their first real glimpse of the girls’ brains. The medical team practiced the procedure on a model designed from images.

How much separation was accomplished Wednesday depended on the complexity of blood vessels, tissue and bone connections.

The girls’ parents, the Rev. Alin Dogaru, a Byzantine Catholic priest, and Claudia Dogaru, both 31, have said they view the separation surgeries as the girls’ best hope. They arrived in Cleveland on April 6 after 2« years in Dallas.

Twins born joined at the head – known as craniopagus twins – are rare, occurring in about one in 2.5 million births. The top of Tatiana’s head is attached to the back of Anastasia’s, and they have never been able to look directly at each other.

Last month, doctors succeeded in establishing independent blood flow in the twins by inserting small coils into veins in their brains. That was viewed as a prerequisite for separation surgery.

Bleeding in these procedures is a major risk. Other potential complications include infection, stroke and a buildup of fluid in the brain, doctors say.