13/04/2016 5:09 PM AEST

Conjoined Sisters Connected At Waist Successfully Separated In Rare Surgery

Ximena and Scarlett Hernandez-Torres are 11 months old.

Associated Press
Conjoined sisters Scarlett, left, and Ximena Hernandez-Torrez were successfully separated at Driscoll Children's Hospital in Corpus Christi this week. 

Following months of preparation and 15 hours of complex surgery, conjoined sisters Ximena and Scarlett Hernandez-Torres were successfully separated this week at a Corpus Christi, Texas hospital.

The girls’ family announced their relief on Facebook on Tuesday night:

Scarlett and Ximena were born as part of a triplet set on May 16, 2015. Connected below their waists, the two girls shared a colon and bladder. (Their sister, Catalina, was born without any serious health issues.)

According to Driscoll Children's Hospital, where the girls' surgery took place, the chance of a triplet birth involving conjoined twins is 1 in 50 million.

The overall survival rate of conjoined twins is said to be between 5 and 25 percent.

Doctors at the hospital have been preparing for the girls' separation surgery for months.

“This is an extremely challenging operation, but we look forward to a successful outcome,” pediatric surgeon Dr. Haroon Patel told ABC News in March.

Surgery to separate conjoined twins is always risky, but it was especially complicated in this case, said Patel, because of the way the babies were connected.

"This arrangement is fairly rare, in only about 6 percent of conjoined twins," Patel told CBS News. "The last time something was published like this in the U.S. was 1966."

On Tuesday morning, the girls were wheeled into surgery, which involved several specialists from urology, plastic surgery and orthopedics. The sisters were successfully separated before undergoing reconstruction surgery, their family said.

According to CNN, this is the first time Driscoll Children's Hospital has separated conjoined siblings.