Conjoined twins Knatalye Hope Mata (R) and Adeline Faith Mata are pictured with their mother Elysse Mata at Texas Children's Hospital in Houston in this July 25, 2014 handout photo obtained by Reuters October 9, 2014.[Photo/Agencies]

The twins' mother, Elysse Mata, and her husband, John, moved across Texas to Houston last year to be near their daughters. She said they were "so grateful to all of the surgeons and everyone who cared for our daughters and gave them the incredible chance to live separate lives".

The couple also has a 5-year-old son.

The condition of the unborn girls was discovered during a routine ultrasound in January 2014. They weighed a combined 3.12 kilograms at birth, or 1.56 kilograms each. They have since been in the hospital's neonatal intensive care unit, and each has grown to more than 9 kg.

"Seeing the girls wheeled out of the operating room as separate patients, on separate gurneys, the ramifications for them to live private lives was even more poignant and powerful than I expected," said Cass, co-director of Texas Children's Fetal Center and associate professor of surgery, pediatrics and obstetrics and gynecology at Baylor College of Medicine. "It literally brought tears to my eyes."