Conjoined twins Nima and Dawa successfully separated at Royal Children’s Hospital in Melbourne

Doctors faced a difficult challenge separating the girls; until the first cut was made, they didn’t know how many organs the twins shared.

It was known that the 15-month-old girls were joined via their shared liver, but doctors said they would not be able to tell if they also shared a bowel until the surgery began.

The worst-case scenario would have been if the girls shared a component that was vital to both. “But there is nothing on the image that suggests that,” Dr Crameri said.

Dr Crameri said one of the risks was the use of anaesthetic, as they did not know how one twin would react to the other receiving it.

On Thursday afternoon, the twins travelled to Melbourne from Kilmore, where they had been staying at the country retreat of the Children First Foundation.

They headed into the theatre at 8am on Friday, and doctors planned to administer the anaesthestic about 8.45am.

From that point on, to avoid confusion, Nima was known as “Green” and Dawa as “Red”. All the doctors, nurses and surgical equipment assigned to each girl were also colour-coded.

The charity’s chief executive Elizabeth Lodge said the toddlers’ mother Bhumchu Zangmo was feeling “a little bit scared” about the operation, but was otherwise in good spirits.

She spent Friday praying and meditating.

“She just wants that quietness and finds it peaceful,” Ms Lodge said.

“She still has this extraordinary calmness about her, which is just amazing.”

Dr Crameri said if there were any unexpected problems during the operation, the hospital had all the resources and experts on hand that it would need.

One of the biggest operating theatres was commandeered for the procedure, which involved two teams of anaesthetists – one for each sister.

The doctors planned to split the surgical team in half once the initial separation was complete.

About 18 people were in the operating theatre – including Bhutanase paediatric surgeon Dr Karma Sherub, who flew into Melbourne this week.

Dr Sherub first met the girls when they were only a day old and played a major role in getting the twins to Australia, having already spent time in the country as the winner of a medical scholarship.

Nima and Dawa were born by caesarean section on July 13 last year in a regional hospital in the Himalayan Kingdom of Bhutan, shocking doctors and the twins’ family who had been expecting twins, but did not know they were conjoined.

It is expected the girls will spend about a month in hospital following the surgery and Dr Sherub previously told The Age that they may take time to catch up with some of their milestones.