Doctors at a Kentucky hospital have successfully separated infant conjoined twin girls.

Kosair Children's Hospital in Louisville said in a statement that the eight-hour surgery was performed on the seven-week-old girls on November 11.

While both remain on ventilators, the hospital said they are getting stronger each day.

The girls were joined at the chest and abdominal cavity. They shared some heart structures and their livers were connected, according to the statement.

Doctors waited as long as they could to perform the risky procedure, making the decision to move forward because both girls needed increased breathing support.

'One of the infants was more fragile than the other, and survival was in question,' according to the release.

Although their long-term prognosis is unknown, chief cardiovascular surgeon Erle H. Austin III says doctors are 'cautiously optimistic' about their future.

'In any situation where you have so complex a surgery, there is always a long road to recovery,' Austin said in a news release.

'We are cautiously optimistic, as one or both may require additional surgeries in the future.'

More than 45 doctors, nurses and hospital staff were involved in the planning procedure to separate the girls whose names have not been released.

Included in that number was a medical team from the University of Louisville Physicians with several types of surgeons and numerous specialists from Kosair.

The hospital would not reveal whether the twins are from Louisville or elsewhere, and their parents declined to be interviewed.

'We are so thankful to God and everyone at Kosair Children's Hospital for getting them this far,' the mother said in the hospital's release.

The children's hospital last separated conjoined twins in 2001.

Those infants were connected at the heart and were unable to survive, according to the hospital.

Experts say conjoined twins occur once in about every 200,000 pregnancies.