Another set of conjoined twins are expected to be born this week in Canada.
The twin girls are joined at the head and doctors at the Vancouver hospital say the birth will create special challenges for the medical team, but it is too early to tell whether it will be possible to separate them.
Ultrasound examinations show the twins heads are fused at the back and at the side, and they appear to share two lobes of the brain.
Dr. Doug Cochrane, a pediatric neurosurgeon, at the B.C. Women's Hospital and Health Centre, says the extent to which blood vessels in the brain are also shared, a crucial factor in determining whether the twins can be safely separated, is at this juncture unknown.
Dr. Cochrane says he expects it will be several months before a decision on the feasibility of a separation is reached.
He says some conjoined twins are not separable without substantial risk to one or both, which creates a series of ethical dilemmas and should a decision be made to separate the twins, they could face as many as 20 operations.
The twins will be delivered by caesarean section by a medical team of 16 specialists in a full operating room at the hospital.
The operation will require a large, L-shaped incision as both heads need to come out at the same time, along with two sets of shoulders.
Within seconds of their birth, the girls will be placed in the care of a neonatology team led by Dr. Brian Lupton, a Neonatal specialist.
They have been in the womb for 34 weeks, which means they will be premature and may need help breathing.
Dr. Lupton, says they have rehearsed the procedures that may be needed to work on two tiny mouths so close together and equipment has been modified to cope with the situation, which means there is two of everything and everyone.