ROCHESTER, MINN. ? Conjoined twins from North Dakota were successfully separated Wednesday.

Dr. Christopher Moir says sisters Abygail and Madysen Fitterer – born joined at chest – were both doing very well after about seven hours of surgery at the Mayo Clinic in Rochester.

“This is Day 99 of their hospital stay. It is also Day 1 of their beautiful, separate lives,” Moir said at a news conference attended by the girls’ parents, Stacy and Suzy Fitterer, of Bismarck, N.D.

The girls rode into the operating room on the lap of their mother, who sat in a wheelchair, just before 7 a.m. Surgeons made the first incision about 9:50 a.m.

According to Mayo experts, conjoined twins may develop in as many as one in 50,000 pregnancies, but account for only one in about 250,000 live births.