Conjoined twins are identical twins that have not split properly after fertilization. Identical (or monozygotic) twins are created from a single fertilized egg. This egg usually separates a few days after fertilization, creating two separate embryos. However, if this egg does not separate within 12 days of separation, it will not split completely. Instead of creating two separate embryos, the two embryos will remain attached in certain areas, causing the babies to grow into one another.
The History of Conjoined Twins
Unfortunately, the history of conjoined twin babies is a sad one. Sometimes referred to as Siamese twins, conjoined twins were often treated as outcasts by society. Unable to get work or support, many conjoined twins were forced to join traveling circuses in order to make a living. The most famous conjoined twins were Eng and Chang Bunker, who were born in Thailand (then called Siam) and worked for Barnum and Bailey’s circus and sideshows. Thankfully, science has allowed for conjoined twins to become understood and accepted by society, and they are no longer exploited.
How Common Are Conjoined Twins?
Conjoined twins are not a very common occurrence. In fact, only about 1 set of conjoined twins is born for every 400,000 live births. The majority of conjoined twins are stillborn or unable to survive more than 24 hours after birth. This is due to the fact that conjoined twins typically share vital organs. Only about 5% of conjoined twins actually survive longer than 24 hours. About 70% of conjoined twins are female, though the reason for this is unknown. It is thought that female embryos may be h2er than male embryos, and are thus able to survive development in utero.
Why do Twins Become Conjoined?
Researchers still do not know why some twins become conjoined. There may be specific genetic reasons responsible for delaying the fertilized egg from splitting into two embryos. There may also be environmental reasons that prevent the egg from splitting completely. More research is required in order to determine the cause of conjoined twins.
Types of Conjoined Twins
Conjoined twins are classified according to where on their bodies they are attached. Types of conjoined twins include:
Craniopagus: These twins are attached at the rear of the head.
Rachipagus: A rare type of conjoining, this occurs when twins are attached at the spine.
Parapagus: This occurs when twins are attached at the side of the pelvis or stomach.
Pyopagus: Another rare type of attachment, this occurs when the twins are united at the pelvis.
Cepalopagus: These twins are joined at both the head and chest, and unfortunately, rarely survive.
Ischiopagus: This occurs when twins are attached at the front of the pelvis. They share genitals, kidneys, a bladder, and their intestines.
Omphalopagus: Accounting for 33% of all conjoinings, this occurs when twins are attached at the abdomen.
Thoracopagus: The most common type of conjoining, this occurs when the twins are attached at the chest. They often share a heart.
Parasitic: Parasitic twins have extra limbs or heads. This occurs when one twin dies in utero, and is absorbed by the other twin.
Testing for Conjoined Twins
Your health care provider should be able to detect any physical attachment between twins using an ultrasound. Ultrasound exams after the 20th week of pregnancy will allow for the detection of conjoined twins and this information can then be used in order to plan for labor and delivery. If your twins appear to be conjoined in utero, it is possible that you will go into preterm labor. Your health care provider will monitor you and your twins to ensure that pregnancy progresses as it should.
Caring for Conjoined Twins
Caring for conjoined twins can be very challenging. Those conjoined twins that do survive often have serious physical challenges. If they share limbs or organs, conjoined twins may be unable to move on their own, eat on their own, or control their own brain or heart function. In many cases, one twin relies solely on their sibling for nutritional, blood, and brain support. In some cases, separation of conjoined twins is considered in order to increase the quality of the twins’ lives, or to save their health.
Separation
Separation of conjoined twins is usually performed when the children are still very young. Typically performed between six and 12 months of age, separation involves a complex series of surgeries in order to completely detach the twins from one another. In some cases, the brain or the heart must be separated in order to provide each twin with vital organs. To date, about 200 twin separations have been performed. One or both twins survived in approximately 75% of these separation surgeries.
Conjoined twin separation is a highly debated topic, for both ethical and moral reasons. Separation often involves sacrificing one twin in order to save the life of the other twin, and because of this, many see the practice as unethical and immoral. Separation can also lead to severe physical disabilities and permanent brain damage. Additionally, it is possible for both twins to die during the separation procedure. For these reasons, separation is only carried out after rigorous testing and preparation.
Prognosis for Conjoined Twins
Unfortunately, the prognosis for conjoined twins is not very good. The vast majority of conjoined twins are stillborn or die within a few days of birth. However, those that do survive have a better prognosis. Many conjoined twins live well into their 60s, and thanks to new techniques used in separation surgeries, many separated twins go on to lead long and fulfilling lives.
