I have personally seen Siamese twins only once. The babies were born at 26 to 27 weeks gestation - about 13 weeks early - and we knew from prenatal ultrasounds that many of their internal organs, such as their liver, were shared, although their hearts were separate. I was the attending neonatologist at their delivery and subsequent admission to the NICU. When they were born it turned out they were fused from their chins down through their chest. Their heads were thrown back by the fusion, their necks permanently extended. They were born alive, with beating hearts, but without much breathing effort or other signs of life. What to do? Their heads and neck were such that it would have been difficult to intubate them and put them on ventilators if we wanted to. We didn't know if their lungs were fused or anomalous in some other way, besides being premature. It was a number of years ago, and the survival rate for babies at that gestation, which is now about 80% to 90%, was less then, and much less for very premature babies with major birth defects. The parents were aware that they might be so severely affected they might not survive.
Should I give them a try? Should I attempt to put both on ventilators and call our pediatric surgeons to try to sort out the awkward mess of fused organs? Should I start treatment that, if they survived, would lead to months of hospitalizations, several surgeries with painful post-op periods, and a next to nothing chance of anything near a normal existence?
No. I let them die a quiet, peaceful death.