Monoamniotic twins (“mono mono” twins) are identical twin babies who share the same amniotic sac inside of the uterus. The chance of having a pair of mono mono twins is quite low, at a rate of around 1 in every 10,000 pregnancies.
That is why Ohio Akron General Medical Center made the news on May 10 of this year when Sarah Thistlethwaite gave birth to mono mono twins. The twin sisters even came out holding hands!