Conjoined twins are twins that are physically joined together in the womb. They are quite rare, affecting less than 1% of monozygotic pairs. Early diagnosis is crucial as some patients choose to terminate the pregnancy due to the serious prognosis. The incidence of conjoined twins varies greatly, with an average occurrence of approximately one in every 50,000 to 100,000 pregnancies. Interestingly, conjoined twins are more commonly found in females, with a ratio of about three females to every one male.¹ This condition is more prevalent in sub-Saharan Africa, where it can occur in approximately one in every 400 sets of monozygotic twins, as well as in certain South American countries.²

Diagnosis

In terms of diagnosis, ultrasound, 3D ultrasound, and magnetic resonance imaging play a crucial role in the antenatal identification of conjoined twins. These imaging techniques allow for a careful analysis of the area of fusion and subsequent prognostication. Typically, the diagnosis of conjoined twins can be confirmed around the 20th week of gestation. In cases of twin pregnancies with a single placenta, the absence of separate amniotic membranes, and the presence of polyhydramnios (excessive amniotic fluid), the suspicion of conjoined twins arises. Early diagnosis is crucial as some patients choose to terminate the pregnancy due to the serious prognosis. Conjoined twins occur in approximately 1.5 out of every 100,000 births, and around 50% of them are born alive. Prenatal screening and diagnosis of conjoined twins are typically done using ultrasonography. In some cases, magnetic resonance imaging may be used to assist in the diagnosis. It's worth noting that conjoined twins in dichorionic diamniotic triplet pregnancies are extremely rare.³

Case

The etiology of conjoined twins' formation remains largely unknown, similar to that of identical twins. No specific genetic, environmental, or demographic factors have been identified as being associated with the development of conjoined twins. It is important to note that conjoined twins are always of the same sex, as they are monozygotic, monochorionic, and monoamniotic. The defect in embryogenesis can occur due to the failure of separation of embryonic discs at around 15-17 days or the fusion of two embryonic discs. Furthermore, there are currently no definitive genetic or environmental predisposing factors linked to conjoined twins. Both fission and fusion are thought to contribute to the disease. A monozygotic twin pregnancy cleaves when it occurs more than thirteen days after fertilization.⁴

Types

Each type is characterized by the specific area where the twins are joined. Thoracopagus twins, being the most common type are joined at the chest and upper abdomen, and they often share some degree of heart connection. On the other hand, omphalopagus twins are fused around the umbilicus area and typically involve the lower chest, but they do not share a heart. Thoracopagus variants make up nearly 40% of all types, while omphalopagus accounts for around 32% of cases. There are several types of conjoined twins based on how they are joined together. Some common types also include craniopagus, ischiopagus, and pygopagus. To summarize: Thoracopagus (connected Unique example Siamese twins, which is a unique example of conjoined twins who lived for a long time. They gained popularity being the longest-living conjoined twins, who reached 63 years of age. Among the at the chest) omphalopagus (connected at the abdomen) and craniopagus (connected at the head).²

Characteristics

Conjoined twins are described as having been physically fused during pregnancy and delivery. They share some organs that are vital for survival, like the heart; There is just one placenta and one womb for conjoined twins (one amniotic sac). These twins are physically connected with each other and may share homologous tissues, organs, and even larger parts of their body. In accordance with the site of conjunction they can be grouped in ventrally, laterally, caudally, and dorsally conjoined twins,

Moreover, conjoined twins can indeed have different personalities. Despite being physically connected, each twin has their own individuality, thoughts, and feelings. They can have distinct likes, dislikes, and unique traits, just like any other siblings. It's a fascinating aspect of their lives and highlights the complexity of their shared existence.

Unique example

Siamese twins, which is a unique example of conjoined twins who lived for a long time. They gained popularity being the longest-living conjoined twins, who reached 63 years of age. Among the celebrated conjoined twins are Chang and Eng, born in Siam (present-day Thailand), who became famous while working in an international circus. They were thoracopagus twins, and shared a common liver.¹

Survival rate

Their overall survival rate ranges from 5% to 25%, with about 75% of surgical separations resulting in at least one twin surviving.⁵ A small proportion of such twins who have separate hearts and common pericardium have better survival rates.²

Treatment

The separation success rate stands at approximately 50.6%. Surgical separation of conjoined twins presents significant challenges and risks.⁶ This elective procedure typically occurs two to four months after birth. In emergency situations, the separation of conjoined twins is performed when one twin is in a critical condition and poses a threat to the survival of the other twin. This decision presents an ethical dilemma that requires careful consideration. The surgical and postsurgical management in emergency separations is complex, and ethical and sociocultural factors add further complications to the decision- making process. The decision to proceed with separation often involves high-risk surgeries and can lead to poor outcomes during and after the procedure. The complexity of the case is compounded by sociocultural and religious factors, which further influence the decision-making process.⁶

While the prognosis for conjoined twins is generally low, there is limited evidence on the best method of terminating the pregnancy, especially in later stages. However, recently a successful case of medical termination of thoraco-omphalopagus twins at 23 weeks and 2 days of gestation. The patient opted for medical termination after thorough assessment and counseling. Adequate cervical preparation, pain control, and careful monitoring were crucial for a successful outcome. This experience suggests that medical termination can be safely performed in carefully selected cases of conjoined twins beyond 20 weeks of gestation.⁷

Conclusion

Conjoined twins are an extraordinary phenomenon that continues to captivate researchers and medical professionals alike. Their intricate physical connection presents complex challenges, but advancements in medical technology and expertise have led to remarkable success stories. Through meticulous planning and multiple surgeries, teams of skilled doctors have achieved successful separations of conjoined twins with fused organs and cavities. These groundbreaking procedures not only save lives but also provide valuable insights into the complexities of human development. The resilience and determination displayed by both the twins and the medical teams involved are truly awe-inspiring.