Dorsal or rear union at the head. Separation is possible although brain damage is common.
Dorsal or rear union at the spine.
Very rare incidence.
lateral or side union with variety with third and fourth limbs. Separation is possible, although a life with artificial limbs is the result.
Dorsal or rear union at pelvis. The incidence of these twins is rare, but the survival and outlook is good.
Ventral or frontal union including the head and chest. Two faces on the opposite side of the head characterize the union. These twins do not survive.
Ventral or frontal union at the pelvis, often with shared intestines, bladders, genitals and kidneys. Separation survival rate is good, although excretion and sexual functions can be impaired.
Ventral or frontal union at the abdomen. Often with shared liver tissue. This type of twins has the highest survival rate. Liver tissue is the only body organ that can regenerate itself, making separation of the liver possible.
Ventral or front union at the chest, often with a shared heart. This type of twins does not survive, although separation has been attempted.
Additional limbs or torsos or heads, believed to be caused by the death of one twin in utero.