Conjoined twins are extremely rare, thought to occur in one in about 200,000 live births

LAST WEEK, a particularly special set of newborn twins were centre stage at a media photocall and made the front pages of several Irish newspapers. Born at University College Hospital in London in December, conjoined twins Hassan and Hussein Benhaffaf were transferred to Cork University Maternity Hospital and made their official public appearance a few days before leaving for home.

While it’s hoped the media will now respect the family’s privacy as they settle in with the new babies, the interest surrounding the boys’ arrival is hardly surprising: conjoined twins are extremely rare, thought to occur in one in about 200,000 live births.

One of the earliest accounts of conjoined twins dates back to AD 945 in Constantinople, and describes twin boys who were probably joined at the chest.

Another pair of conjoined twins were reportedly born in 1100 in Biddenden in Kent, England: Mary and Eliza Chulkhurst were known as the Biddenden Maids and were said to be joined at the hip.

Accounts state that they lived to the age of 34 when one sister died of an illness – the other sister refused to be separated from her twin and died shortly afterwards.

Whether the Biddenden story is true or accurate is a debate for historians, but the twins’ legendary generosity to the church inspired centuries of charity and cakes made in their image.

A more recent and more reliably documented pair of conjoined twins became famous in the 19th century. Chang and Eng Bunker were born in 1811 in Thailand, then called Siam.

Joined at the torso, they were successful entrepreneurs and toured around the US and Europe, and their fame gave rise to the formerly used term “Siamese” twins, which is no longer considered appropriate.

The brothers, who married two sisters and had several children, died aged 63 and are buried in North Carolina, where they had a plantation.

That US state was also home to Millie-Christine McKoy, conjoined twins born in 1851, who were joined at the lower backbone and who often referred to themselves as a single person.

Millie-Christine’s parents were slaves and their landowner sold the twins for exhibition, so they ended up travelling the world singing and reciting poetry. They died in 1912 after Millie contracted tuberculosis.

As the 20th century progressed so did surgical techniques, and medical teams carried out landmark successful separations, including that of Clara and Altagracia Rodriguez from the Dominican Republic in 1974.

US surgeon Dr C Everett Koop led a team who separated the 13-month-old sisters who shared a liver and part of the colon, and whose connection meant they could not walk or sit properly. Only a handful of medical centres around the world have built up considerable multidisciplinary experience in assessing and separating conjoined twins, including the Children’s Hospital of Philadelphia and Great Ormond Street Hospital for Children in London.

And just as Ireland’s newest set of conjoined twins leave the media spotlight to settle in at home, the Associated Press reports that the world’s oldest documented living conjoined twins are also on the move.

Aged 58, twins Donnie and Ronnie Galyon in Dayton, Ohio, are joined at the torso and are going to live with their brother Jim, who will help to look after them.

CONJOINED TWINS: THE FACTS

Conjoined twins are always identical and arise from a single fertilised egg. As with other identical twins, the fertilised egg develops and starts to split to form two separate embryos. But in the case of conjoined twins, the prevailing theory holds that the splitting process doesn’t fully complete and babies that eventually develop are conjoined.

Such pairs of conjoined twins are usually classified according to their fusion site and several have been identified, including the chest, bellybutton, base of the spine, pelvis and head.

Many conjoined twins do not survive birth, and of those who do, the decision separate them by emergency or elective procedures is influenced by the nature of the fusion and whether they share vital organs.