Siamese Twins / Conjoined Twins

Bellaflores, Marc Gideon L.DMD2D

What are Siamese Twins?

Conjoined twins are identical twins that have not split properly after fertilization, they share a body and may share vital organs.

Identical twins are created from a single fertilized egg.

If the egg does not separate within 12 days, it will not split completely.

Instead of creating two separate embryos, the two embryos will remain attached, causing the babies to grow into one another.

History of Conjoined Twins

A popular term for conjoined twins is “Siamese twins”

The term comes from Eng and Chang Bunker who were famous conjoined twins born in Siam in 1811.

The term “Siamese twins” is no longer considered appropriate because they aren’t limited to any racial or ethnic group.

Are Conjoined Twins Common?

Conjoined twins are not a common occurrence.

Only about one set of conjoined twins are born every 400,000 births, but only once in every 200,000 LIVE births.

Are more likely to occur in India or Africa than in China or the United States.

Conjoined twins are more often female than male, at a ratio of 3:1 or 70%.

Types of Conjoined Twins

Thoraco-omphalopagus (28% of cases):[7] Two bodies fused from the upper chest to the lower chest. These twins usually share a heart, and may also share the liver or part of the digestive system.[8]

Thoracopagus (18.5%):[7] Two bodies fused from the upper thorax to lower belly. The heart is always involved in these cases.[8]

Omphalopagus (10%):[7] Two bodies fused at the lower chest. Unlike thoracopagus, the heart is never involved in these cases; however, the twins often share a liver, digestive system, diaphragm and other organs.[8]

Parasitic twins (10%):[7] Twins that are asymmetrically conjoined, resulting in one twin that is small, less formed, and dependent on the larger twin for survival.

Craniopagus (6%):[7] Fused skulls, but separate bodies. These twins can be conjoined at the back of the head, the front of the head, or the side of the head, but not on the face or the base of the skull.[8]

Separation

Separation of conjoined twins is usually performed at a very young age.

In some cases the brain or the heart must be separated in order to provide each twin with vital organs.

To date, about 200 separations have been performed.

When to Separate

In the past, surgery was delayed until twins were 6-12 months old so that they could become stronger.

Since there are now life-support systems and diagnostic tools are more sophisticated, earlier separation is more common.

Immediate separation is needed when one twin is stillborn.

Separation while twins are too young to realize that they are joined is thought to help their psychological recovery.

Dental Correlation

• When conjoined twins are not separated all administered drugs are calculated on a total-weight basis, with half being delivered to each twin

• But most conjoined twins now a days are separated so a normal dental procedure is given to them

Classification

• I classify Conjoined twins into Mendelian genetics because sometimes Some twins fraternal or dizygotic twins only are the result of hyperovulation, a female tendency to release multiple eggs during ovulation. If two or three or more eggs are fertilized and implant, the result is twins or multiples. Hyperovulation can be a genetic tendency, so if a mother has the gene for it, her daughter might also. In that sense, it can be said that twins run in the family, but on the mother's side only. Fathers don't ovulate, so they don't impact twinning in this scenario.