The operation for Eva and Erika Sandoval of Antelope began at 6am and was expected to last between 18 and 24 hours.READ MORE: San Jose Police Arrested Two For Trafficking Illegal 'Ghost Guns'
The rare operation will involve 50 hospital staff, and 3-D printed models of the 2 year old girl’s fused pelvis and blood vessels.
Doctors say there is a 30 percent that one or both of the twins will not survive.READ MORE: COVID: Healdsburg Family Leaving California On Cross-Country Trip In Search Of New Home
The biggest threat to their survival is blood loss.
The girls have separate brains and hearts but they share a liver, bladder, and some of their digestive system.MORE NEWS: Royals Week: Recent San Francisco Bay Area Visits – A Combination Of Pomp And Protest
Even though the twins are thriving together doctors say they surgery is needed for their long term health.