Types of Conjoined Twins

Maria and Teresa Tapia
Conjoined twins Maria and Teresa Tapia. Photo courtesy of World Pediatric Project

What are Omphalopagus Twins? 

Omphalopagus twins are a classification of conjoined twins. They are one of the most common types of conjoined twins, representing about one-third of conjoined twins. Conjoined twins are classified by the location of their connection. In the case of omphalopagus twins, they are connected at the abdominal region. These individuals share an anterior connection of the trunk, usually at the abdomen, but the connection can range from the thorax down to the umbilicus.

 Usually, omphalopagus face each other. There are four arms, four legs, and two pelvises. Omphalopagus twins may share a liver, gastrointestinal or genitourinary functions. 

Omphalopagus twins are differentiated from thoracopagus twins because they do not share a heart.  They are differentiated by ischiopagus twins, who are also joined at the pelvis, based on the angle of the spine; ischiopagus twins have two separate spines forming a lateral angle smaller than 90°.

How are Omphalopagus Twins Diagnosed?

Visual confirmation by ultrasound can identify conjoined twins and determine details about the location of the connection. When conjoined twins are suspected, magnetic resonance imaging (MRI) can provide a clearer picture of the situation. Other assessments, such as an echocardiogram may provide further information about how the twins are connected. In some cases, omphalopagus twins are not confirmed until after delivery.

Prognosis for Omphalopagus Twins

The prognosis for omphalopagus twins varies depending on the twins' individual circumstances. Overall, the prognosis for conjoined twins is grim. Almost half are stillborn. For those that survive to be delivered, many face life-threatening complications. The outcome is determined by the degree of connectivity; omphalopagus twins that share vital organs are more likely to succumb to complications.

The more that twins share, the more difficult it for them to survive or to be surgically separated. However, among classifications of conjoined twins, omphalopagus twins face the best odds, particularly if each individual has separately functioning organs. 

Examples of Omphalopagus Twins

Because omphalopagus twins are the most common type of conjoined twins, there are many examples to note.  In many cases, surgical separation of omphalopagus twins can be successfully completed. Here are some examples: 

  • Tiesha and Iesha Turner: The Turner twins were born in Texas in 1991. They shared a sternum and liver. Their intestines were entwined. Although they had individual hearts, the organs were fused together. They were separated at Texas Children's Hospital in Houston, Texas on June 9, 1992. In a follow-up interview in 2007, the girls were reported to be healthy, normal high school students. 
  • Andrew and Alex Olson: These twin boys were born in South Dakota in 1987. They shared a liver and their intestines were entwined; each boy had an autonomous leg and shared a third. They underwent separation surgery at the University of Nebraska Medical Center in April 1988. 

    Each boy lost a leg in the separation. 


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