1. Conjoined Twins
Julia Kudryashova

2. What are conjoined twins?
Conjoined twins are two babies that are born physically connected to each other
These twins develop when a single fertilized egg only partially splits
Two fetuses will develop from this egg
Conjoined twins may also share one or more internal organs

3. Formation Theories
Fission theory: conjoined twins occur when a fertilized (egg) begins to split into identical twins, but is somehow interrupted during the process and develops into two partially formed individuals who are stuck together

4. Fusion Theory
Twins become conjoined after the fertilized ovum initially splits into identical twins.
While lying side-by-side in the uterine wall, the two embryos become fused together.
A human embryo, in its earliest stages, consists of three layers of cells.
These cells "seek out" cells of the same type and thus bond together to form individual organs.
When two newly-separated identical twin embryos are lying in close proximity to one another, sometimes signals get mixed and cells will attach to other cells of the same type, but that belong to the other twin.

5. Three most common types of conjoined twins:
Thoracopagus: Joined at the upper chest, from the clavicle to the sternum, each with their own separate heads, arms, and legs.
Physiological Problems:
Some thoracopagus twins have two separate hearts while others have a single malformed heart
Separation is extremely risky and both twins often die
Thoracopagus twins are the most common type, accounting for around 35% of all cases.

6. Omphalopagus twins
Joined at the abdomen, from the sternum to the groin and often sharing a liver and portions of the digestive system.
These twins have separate hearts, heads, arms and legs.
Separation is usually successful.
About 30% of cases.

7. Ischiopagus Twins
These twins are joined at the front pelvis and lower spine, with spines at 180-degree angles to one another.
These twins can have three legs or four legs. About 70% of ischiopagus twins have four complete legs.
In tripus cases, the third leg is a fusion of two legs that is not controlled by either twin and is therefore useless.
About 14% of cases.

8. Surgery to Separate Twins
Most cases of separation are extremely risky and life threatening
In most cases the surgery results in the death of one or both of the twins
Twins joined at the sacrum have a 68% chance of successful separation unlike twins with conjoined hearts- no known survivors
The ethics of surgical operation is questioned when twins are joined at the head
The operation becomes controversial because usually the weaker twin of the two dies

9. After Separation
Most twins need intensive rehabilitation because of the malformation and position of their spines
The muscles in their backs are constantly being flexed and they often have a difficult time bending their backs forward and backwards and sitting up straight