A Barcelona hospital said Monday it had successfully separated a pair of seven-month-old conjoined twins who shared a liver.

Nuria and Marta, who were born on August 10 and were joined at the abdomen, underwent a seven-hour "complex and painstaking" operation on February 27, the Vall d'Hebron hospital said in a statement.

They now "lead a normal life and come to hospital only for routine checks," it said.

Conjoined twins are an extremely rare phenomenon -- with one for every 200,000 births, the hospital said, adding that the chances of survival at birth ranged from 5 to 25 percent.