There is an extremely rare form of identical twins that occurs perhaps in one out of every 75,000 to 100,000 births or 1 in 200 deliveries of identical twins, that of conjoined twins.
Conjoined twins originate from a single fertilized egg so they are always identical and same-sex twins. The developing embryo starts to split into identical twins within the first two weeks after conception but then stops before completion, leaving a partially separated egg which continues to mature into a conjoined fetus.
|The most famous
set of conjoined twins were Chang and Eng, the men who originated the term
"Siamese Twins". Eng and Chang were born in Siam (modern day Thailand) on May 11,
1811 to a Chinese father and half-Chinese, half-Malay mother. Thanks to
their heritage, while growing up in Siam the boys were known as
"The Chinese Twins".
Despite the fact that their birth was initially believed to be an omen of the end of the world, they brought celebrity to their small village. Their mother refused to allow doctors to attempt to separate the boys, fearing that to do so would result in the death of one or both. Instead she taught them to stretch the tissue that joined them so that they could stand side-by-side rather than always face-to-face.
In 1824, Scottish merchant Robert Hunter discovered the twins by accident while they were swimming. He introduced himself and became a friend of their family. Later he asked the Siamese government for permission to take the boys to Europe, but his request was at first denied.
In 1829 Hunter and his associate Captain Abel Coffin offered money to the boys' mother for permission to take them abroad, then tried again with the government; this time they succeeded. In April, 17 year-olds Chang and Eng left for Boston, excited to see the world.
After a successful and profitable tour of the States, the group then sailed to England where they became quite popular. They were extensively examined by doctors and visited by royalty.
Unfortunately, their next planned stop, France, did not receive them quite so well; they were denied entry by the French government. The rest of Europe, however, was not closed to them, so they toured extensively, continuing to pack venues.
In 1832 Chang and Eng broke off their arrangement with Captain Coffin (Mr. Hunter having sold his share of the rights to Coffin while they were in Europe) when they realized that he was taking the vast majority of the money received for their tours. This break led them to P. T. Barnum, with whom they toured until 1839, when they decided to quit the exhibition life and settle down.
They chose Wilkesboro, North Carolina where they began the life of farmers. In 1839 they became United States citizens, but lacking last names they were simply listed as "Chang and Eng, Siamese Twins." In 1844 they decided to remedy that by petitioning to adopt the name Bunker, although it is not known for sure where this came from.
Chang and Eng began to date Adelaide and Sarah Ann Yates, two of nine daughters of local farmer and part-time clergyman, David Yates. The townspeople disapproved, so Chang and Eng scheduled a separation surgery in Philadelphia. Their fiancées found out and quickly stopped the proceeding, and in April, 1843, Chang was married to Adelaide and Eng to Sarah Ann in a double wedding.
During the course of their marriages, Eng fathered six boys and five girls; Chang seven girls and three boys. All were normal except for a son and daughter of Chang's who were deaf mutes.
In January, 1874, Chang Bunker died after a severe case of bronchitis, possibly from a cerebral clot. Eng died shortly thereafter.
After their deaths it was determined they could have been successfully separated, a medical option that was never offered to Eng and Chang during their lives.
Although Eng and Chang's fame helped coin the phrase 'Siamese Twins', they were not the first pair of conjoined twins recorded in medical annals as there were probably about 100 such pairs known by the time of their 1811 births, a fact which helped the King of Siam reverse an early death sentence on the brothers. In fact, conjoined twins were recorded as early as 945 in Armenia and the first pair of successfully separated twins took place in 1689 by German physician G. König.
The birth of two connected babies can be extremely traumatic and approximately 40-60% of these births are delivered stillborn with 35% surviving just one day. The overall survival rate of conjoined twins is somewhere between 5-25% and historical records over the past 500 years detail about 600 surviving sets of conjoined twins with more than 70% of those surviving pairs resulting in female twins.
While there are dozens of types of conjoined twins, doctors
generally divide the types into the more common variations described in the
below chart. All of these types can be more broadly categorized as displaying
either equal and symmetrical forms or unequal and possible asymmetrical forms.
|Craniopagus||Twins are joined at the cranium (the top of the head or skull). Occuring in just 2% of all conjoined twin cases, this is a very difficult type of twin to separate although advances in medicine have led to more than 35 successful separations. Two female craniopagus twins were successful separated in Lithuania in 1989, for example.|
|Thoraopagus||The most common form of conjoined twins, occuring in between 35-40% of all cases. The twins share part of the chest wall, possibly including sharing the heart.|
|Pygopagus||Twins are likely positioned back-to-back and usually have a posterior connecton at the rump. Occurs in almost 20% of documented cases.|
|Ischiopagus||About 6% of all conjoined twins have this condition, with the twins joined by the coccyx (lowest part of the backbone) and the sacrum (backbone immediately above the coccyx).|
|Omphalopagus||Twins are united from the waist to the lower breastbone, probably accounting for about 34% of conjoined cases.|
|Dicephalus||One body with two separate heads and necks. Abigail and Brittany Hensel of the United States are an example of this very rare type of conjoined twin. The Tocci Brothers, Scottish Brothers and Ritta and Christina were also examples of this type of conjoined twin.|
Several hospitals across the world specialize in these often difficult surgeries. The Children's Hospital of Philadelphia has performed more than a dozen successful separation surgeries since its first operation in 1957 (most recently performing one on 7-month-old twin girls on March 1, 2001), while physicians such as Dr. Rich Hampton of the Pediatric Surgical Associates in the Twin Cities of Minneapolis and St. Paul, successful separated Keri and Kaci Archer in October, 1991. The Children's Hospital of Boston has operated on nine sets of conjoined twins (as of the mid 1990's, current numbers not available).
There are organizations which can help parents of conjoined twins address some of the issues they will face during their pregnancies or while raising their children. Conjoined Twins International, based in Prescott, Arizona, was founded in 1987 by a grandfather of conjoined twins. The organization gives advice and support to a little more than half of the families of conjoined twins currently living in the United States. They can be reached via telephone at 520-445-2770 or via email.