Once-Conjoined Twins Turn 10 - How They're Doing

Josie and Teresa

Josie and Teresa

Mending Kids International

As her friends cheered and applauded, Josie began to tread water like a pro at her 10th birthday party. Her broad smiled spoke to her growing confidence in the pool.

"I'm learning synchronized swimming," Josie says, "and I really like it."

It's hard to fathom that nine years ago, Josie, born Maria de Jesus Quiej Alvarez, was lying in an intensive care unit, clinging to life after surviving a 23-hour surgery at UCLA's Mattel Children's Hospital that separated the Guatemalan 1-year-old from her conjoined twin sister, Maria Teresa.

Famously known as "the Two Marias," they were craniopagus twins – those who are fused at the tops of their heads – accounting for just 2 percent of conjoined cases worldwide.

Their separation surgery made international headlines and required support from Mending Kids International, then a chapter of Healing the Children, which includes such benefactors Mel and Robyn Gibson, who were on hand Saturday when Josie and Teresa celebrated the Hawaiian-themed birthday at a home in Malibu.

"It's incredible," Mel told PEOPLE. "Conjoined twins joined at the head don't normally get to see age 10. It's special seeing them doing as well as they are, and doing it with such joy. But it's not like they don't have hurdles to hop, they do."

Just 10 months after the Aug. 6, 2002 surgery, the girls were airlifted on a donated private jet back from Guatemala for emergency treatment. Teresa had contracted deadly meningitis, and spent five months in 2003 in and out of a coma. Today, she is unable to walk and cannot speak.

The twins in 2002

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