Siamese Twins

Conjoined or Siamese twins have fascinated people for centuries. They have been worshipped as gods and feared as monsters. They play a role in our myths and are marveled at in circus shows. Once called 'monstrosities', conjoined twins are increasingly accepted into our everyday lives as we grow to understand their unusual physical and emotional bonds and learn more about the science behind their development….

Formation of the physical-emotional bond

Conjoined twins are a variation of identical twins, these twins are joined at one or the other body part. This is because of incomplete splitting of the fertilised egg during pregnancy leading to incompletely separated individuals. Conjoined twins are joined at some point in their bodies and may also share some organs. Conjoined twins have been known to be joined from the head, chest, stomach and hips and may share tissues, organs or limbs. Like all identical twins, conjoined twins look alike and are always same sex (either both boys or both girls). It is estimated that 70 % of conjoined twins are female.

These twins may be caused by any number of factors, being influenced by genetic and environmental conditions. It is presently thought that these factors are responsible for the failure of twins to separate after the 13th day after fertilization. Conjoined twins can be artificially generated in amphibians by constricting the embryo so that two embryos form, one on each side of the constriction.

The frequency of the birth of conjoined twins is difficult to estimate, but it's a fairly rare occurrence. Exact statistics are not known, but are estimated to be about 1 in 85,000 births. About 1 in 200 sets of identical twins are born conjoined. Most conjoined twins are stillborn, and those that survive often die within a few hours.

Why ‘Siamese’?

The origin and the historical roots of the term "Siamese twins" can be attributed to Chang and Eng Bunker, the famous conjoined twins from Siam (now Thailand) who earned their living in the U.S. as a circus attraction in the Barnum and Baily Circus. They were born on May 11, 1811 in Siam and eventually made their way to the United States where they earned a living first as circus attractions and then as farmers. As they traveled the world, they became known as "the Siamese twins." While they were the first conjoined twins whose medical history was documented, they were not the first conjoined twins. Records reference a set of conjoined boys living in Constantinople in 945 A.D. Another well-known set, Mary and Eliza Chulkhurst, lived in England in the twelfth century. Chang and Eng lived long and fruitful lives until their death at the age of 63. Both married and fathered 21 children between them. Interestingly, 2 of their grand-daughters produced 2 normal sets of twins.

Types of conjoined twins

There are various types of conjoined twins and are usually classified by the point at which they are joined (the Greek word pagos, meaning "that which is fixed.") There have been as many as three dozen separate types identified in the last century. The following basic classifications can be combined to more closely define individual cases.

  • Craniopagus: Joined at the head, about 2% of all conjoined twins.
  • Pygopagus: Joined at the rear end, about 19% of all conjoined twins.
  • Thoracopagus: These are joined at the chest. The most common form of conjoined twins (about 35%), it always involves sharing the heart.
  • Cephalopagus: Anterior union of the upper half of the body with two faces on opposite sides of a conjoined head. Extremely rare. The heart is sometimes involved.
  • Parapagus (sometimes called diprosopus): There is union of the lower half side to side, extending variable distances upward, about 5% of all conjoined twins. Heart sometimes involved.
  • Ischopagus: There is union of the lower half of the body, about 6% of all conjoined twins. Heart not involved.
  • Omphalopagus: There is union of the midtrunk, about 30% of conjoined twins.
Rare forms of conjoined twins, having different patterns:
  • Parasitic twins: Asymmetrical conjoined twins, one twin being small, less formed, and dependent upon the other.
  • Fetus in fetu: Situation in which an imperfect fetus is contained completely within the body of its sibling.

When the twins share an extensive connection over several areas, then the duplicated part is named. For example, dicephalus describes twins with two heads and one body.

The prognosis...

The prognosis depends on how the twins are connected. It is estimated that 40-60% are born stillborn. 35% survive 24 hours or less. For those that do survive, their parents will face difficult decisions regarding their future. Some conjoined twins live successful lives despite the unique challenges they face. Others are plagued by medical complications due to shared organs and vital systems. The overall survival rate of conjoined twins is between five percent and 25 percent with about 75 percent of the surgical operations since 1950 resulting in one or both of the twins surviving.

And the separation

Since the late twentieth century, many medical advances have resulted in the successful surgical separation of conjoined twins. In the United States, the Children's Hospital of Philadelphia has performed more than a dozen successful separations.

The first successful operation to separate a pair of conjoined twins occurred as early as 1689 by a German doctor, G. Konig. The success rates for separating conjoined twins vary depending on the connection. If the twins have separate sets of organs, chances for surgery and survival are greater than if they share the same organs. Over the years, survival rates have improved as a result of more accurate imaging studies and better anaesthetic and operative techniques.