Sarah Thistlethwaite, from Orrville, Ohio, gave birth to the identical twins, Jenna and Jillian after spending nearly two months in the hospital. The girls, who were born holding hands, shared an amniotic sac and placenta — a rare occurrence that doctors say happens just once in every 10,000 pregnancies, the au news reported.

Thistlethwaite had been hospitalised since March 14 after discovering the unborn twins' "mono mono" condition. While in the hospital, Thistlewaite was hooked up to fetal monitors for 20 hours a day.

"When twins share an amniotic sack, there are many risks to monitor," the Akron General hospital explained in a blog post. "The twins’ umbilical cords can become entangled or compressed. And there’s a risk that one fetus’ cord might wrap around the other one’s neck."

Thistlethwaite opted to have a C-section.

The procedure went smoothly, according to the hospital, with Jenna and Jillian weighing four pounds, two ounces and three pounds, 12 ounces, respectively. Because they were considered premature, the twins were taken directly to the hospital's neonatal intensive care unit, where they're expected to spend two to four weeks before they’re ready to go home.

Meanwhile, "mono mono" twins are apparently becoming something of a trend in Akron: Amanda Arnold, another expectant mother, is due to deliver monoamniatic twins at Akron General next week.