Jillian and Jenna Thistlethwaite shared an amniotic sac and placenta, a rare condition known as monoamniotic birth. "They're already best friends," said their mother, Sarah Thistlethwaite. They were born on Friday in the US state of Ohio, grasping each other's hands when doctors lifted them up for their parents to see after delivery. Monoamniotic birth occurs in only one in 10,000 pregnancies. 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."