- Carrying conjoined twins is extremely rare.
- For some reason, female twins seem to have a better shot at survival than their male twins.
- Approximately 70 percent of all conjoined twins are girls
- Conjoined twins are genetically identical, and are, therefore, always the same sex.
- They develop from the same fertilized egg, and they share the same amniotic cavity and placenta
- The term Siamese twins is no longer considered appropriate.
- Conjoined twins aren't limited to any racial or ethnic group
- There are nearly a dozen different types of conjoined twins.
- Most common is thoracopagus twins. These twins are connected at the upper portion of the torso.
- Thoracopagus twins share a heart, which, depending on how closely they are joined, makes it nearly impossible to separate them and save them both.
- Thoracopagus twins make up about 40 percent of all conjoined cases
- One of the rarest types of conjoined twins is Craniophagus twins, which are joined at the cranium or head.
- There are no documented cases of conjoined triplets or quadruplets
How conjoined twins happen is when, a woman only produces a single egg, which does not fully separate after fertilization. The developing embryo starts to split into identical twins during the first few weeks after conception, but stops before the process is complete. The partially separated egg develops into a conjoined fetus.
Source: University of Maryland Medicine