Ten months later, doctors at Driscoll Children`s Hospital are getting ready to separate them during a procedure that will last 12 to 18 hours, CBS reported.
The likelihood of having conjoined twins as part of a set of triplets is around one in 50 million according to experts at Driscoll.
Not only that, but the way the little girls are connected to each other is a rarity too.
They are joined at the pelvis and have separate legs.
Ximena and Scarlett, who are currently nourished through a feeding tube, only have one colon and share some organs such as the uterus and ovaries, CBS wrote.
The twins have two bladders, but for now Ximena`s kidneys are linked to Scarlett`s bladder, and vice versa.
Only six per cent of conjoined twins are connected this way, Dr. Haroon Patel, who leads the team in charge of the girls` procedure, told CBS.
`The last time something was published like this in the U.S. was 1966,` he added.
Patel`s team includes pediatric and plastic surgeons as well as urology and orthopedic specialists.
They have spent the last few months preparing for the surgery and have created a 3D model of the girls` organs, using it to practice the procedure ahead of time.
During the surgery, they will split Ximena and Scarlett`s colon and give half to each of them, Patel told CBS.
They will also reroute their kidneys to link them to the correct bladder and separate their skin and organs.
Scarlett and Ximena are expected to go home within three months after the surgery, which doctors predict will be a success.
The little girls were supposed to go through the procedure in March, but they caught a respiratory infection that delayed it until April.
Their mother, Silvia Hernandez, 23, has spent the last 10 months at a nearby Ronald McDonald House.
She has divided her time between the twins and their sister, Catalina, the third triplet, as well as their older brother, Raul, who is three years old.
Catalina is doing well according to her mother, who said on Facebook the little girl just wouldn`t let her parents sleep at night.
Hernandez and her husband Raul Torres found out three months into the pregnancy that they were having triplets and that two of them were conjoined.
`Since they were born, I have been waiting anxiously for them to be separated because I want to hold them separately in my arms and hold them close,` Hernandez told CBS.
`But the closer the surgery day is getting, I don`t want it to happen. But of course I want it to happen so they can have a normal life. My daughters are in hands of God and his will will be done.`
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