"They're already best friends,"
"It's just hard to put into words how amazing it feels to know the girls are OK," she told The Associated Press.
The identical twin girls shared the same amniotic sac and placenta. Such births are called monoamniotic, or "mono mono," and doctors say they occur in about one of every 10,000 pregnancies.
They were born Friday in Ohio, grasping each other's hands when doctors lifted them up for their parents to see after delivery.
Thistlethwaite told the Akron Beacon Journal that this was "the best Mother's Day present ever."
"They're already best friends," said Thistlethwaite (32). "I can't believe they were holding hands. That's amazing."
Dr. Melissa Mancuso helped deliver the twins, one of several amniotic pairs she has helped deliver in 11 years. She said the twins are at risk during pregnancy of entanglement of umbilical cords, which can cause death.