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Jillian and Jenna Thistlethwaite were breathing on their own after being removed from a ventilator, their mother, Sarah Thistlethwaite, said.
The girls shared an amniotic sac and placenta, a rare condition known as monoamniotic birth, BBC reports.
They were born in Ohio at the weekend, grasping each other's hands when doctors lifted them up for their parents to see after delivery.
"They're already best friends," said their mother,
Ms Thistlethwaite, 32, was monitored for weeks at Akron General Medical Center in Akron, as monoamniotic twins are at risk from becoming entangled in each other's umbilical cords.
She told the Akron Beacon Journal newspaper that holding her children was "the best Mother's Day present ever".
"I can't believe they were holding hands," she said. "That's amazing."
Monoamniotic birth occurs in only one in 10,000 pregnancies.