Surgery has started in Texas to separate two 10-month-old sisters born conjoined below the waist.

Driscoll Children's Hospital spokesman Jeff Salzgeber says the hours-long operation began on Tuesday morning in Corpus Christi.

Ximena and Scarlett Hernandez-Torres share a colon and bladders that will be reconstructed, however have their own legs.

Their identical triplet sister, Catalina, was born without serious health issues.

Undergoing surgery: Ximena and Scarlett Hernandez-Torres share a colon and bladders that will be reconstructed. The conjoined twins headed in for surgery in Corpus Christi on Tuesday morning

Driscoll Children's Hospital staff has cared for the girls since they were transferred to the facility last year

The girls were actually born triplets, with their identical sister, Catalina, born without any major health issues

The hospital staff has cared for the conjoined girls since they were transferred to the Corpus Christi facility hours after birth.

Dr. Haroon Patel says a team of 45 specialists has been working for months to prepare for the surgery, which could last 12 to 18 hours.

A hospital statement says doctors have a positive outlook for the children's recovery.

The girls will require additional surgeries as they grow.

Ceremony: The girls were baptized Saturday at the hospital in preparation for the surgery, as per their parents wishes

Triplets Ximena, Scarlett, and Catalina were born in May last year. Ximena and Scarlett are joined at the pelvis, but have separate legs. Catalina was born without any major issues

The girls were baptized Saturday at the hospital in preparation for the surgery.

'I'm nervous,' their father Raul Torres told NBC News.

'I've been praying a lot, every single day, even at work I think about them and think about the surgery. Sometimes I can't even sleep.'

'Just in case something happens like that, their soul can already be with God, before something bad happens.'

There is only a one in 50 million chance that conjoined twins are born in a set of triplets.

Rare: Experts say the chances of having conjoined twins in a set of triplets are one in 50 million