Dicephalic Parapagus Dibrachius Tripus Conjoined Twins: A Case Report of an Unusual Twinning Phenomenon

ABSTRACT

Dicephalic parapagus conjoined twins are a rare congenital anomaly with a poor prognosis. Early prenatal detection via ultrasonography is necessary for optimal management. Termination is often recommended, with vaginal delivery considered before 24 weeks of gestation and cesarean section preferred for term or near‐term pregnancies.

1. Introduction

Conjoined twins are a rare embryologic developmental anomaly. In the largest study on conjoined twins, Mutchinick et al. reported a global prevalence of 1.47 per 100,000 births, with a notable female predominance (2:1 ratio) [1]. Conjoined twins are classified based on the most prominent site of union, denoted by the suffix “‐pagus,” meaning “fixed”. For instance, parapagus twins are joined laterally and often share the pelvis [1, 2].

Two primary theories—fission and fusion—have been proposed to explain their formation. The fission theory suggests incomplete division of the embryo due to disrupted cellular processes, whereas the fusion theory proposes partial fusion of two distinct embryonic discs [3].

Ultrasonography and magnetic resonance imaging (MRI) are crucial for the prenatal diagnosis of conjoined twins, as they avoid ionizing radiation. Prenatal counseling, obstetric management, and delivery planning all rely heavily on these diagnostic tools. Ultrasound can detect conjoined twins as early as 12 weeks of gestation; however, a comprehensive evaluation of visceral fusion can only be performed at 20 weeks [4].

Here, we report a rare case of dicephalic parapagus conjoined twins diagnosed during the second trimester via ultrasonography and confirmed postnatally (Figure 1). Following counseling regarding the prognosis and management, the parents opted for pregnancy termination. This case highlights the diagnostic and management challenges in resource‐limited settings, particularly when advanced imaging modalities like MRI are unavailable. It also highlights the complexity of managing a conjoined twins pregnancy detected at 20 weeks of gestation. Our article has been reported in line with the CARE guidelines [5].

FIGURE 1.

External characteristics of dicepahlic parapagus twins. (A) Conjoined twins with placenta delivered after induced abortion. (B) Vental view showing two heads, a shared thorax with a single umbilical cord, two upper extremities, and three lower extremities. Two lower extremities are in the normal position, while the third is abnormally positioned. (C) Dorsal view showing the normal positioning of the heads with the left twin having a smaller head and a shorter neck. The two upper extremities arise from the normal position. The third lower extremity arises from the dorsal end/lumbo‐sacral region and has a dysmorphic foot. (D) Close‐up of the dysmorphic foot showing eight toes, with the big toe arising from the mid‐dorsal aspect of the foot. (E) Showing one penis (white arrowhead).

2. Case History and Examination

A 25‐year‐old primigravida presented for her first antenatal checkup at 19 weeks and 4 days of gestation, based on the first day of her last menstrual period. An anomaly scan revealed dicepahlic parapagus conjoined twins. She reported no abdominal pain, vaginal bleeding, or leaking, and perceived adequate fetal movements. Married for 2 years, she conceived naturally, confirmed by a urine pregnancy test at 6 weeks. There was no history of assisted reproduction. She had not taken folic acid, iron supplements, Td vaccine, or deworming tablets during her pregnancy due to a lack of awareness. Quickening was reported at 18 weeks of gestation.

Her menstrual cycles were regular, with normal flow lasting 3–4 days and associated with dysmenorrhea. She had no significant past medical history, nor any family history of congenital anomalies, stillbirths, or twin pregnancies. She had never used contraceptives.

On presentation, her general condition was fair and vitals were stable. General and systemic and general examinations were unremarkable. Obstetric examination revealed a fundal height of 20 cm and a single fetal heart sound of 140 beats/min on Doppler. Pelvic and per speculum examinations were normal.

3. Differential Diagnosis, Investigations, and Treatment

Ultrasonography showed a single live intrauterine fetus with gross anomalies, including two heads, one torso, and two vertebral columns. The fetus had normal cardiac activity, a fundo‐anterior placenta, breech presentation, adequate amniotic fluid, and an estimated fetal weight of 377 g. The right‐sided twin showed dilated lateral ventricles (maximum diameter 9.6 mm), right‐sided hydronephrosis, and an enlarged bladder.

Although ultrasonography was the primary diagnostic tool, it could not determine the extent of fusion or the details of shared internal structures. Due to resource limitations, fetal echocardiography and MRI were not performed. The parents declined referral to a higher center due to financial constraints. After counseling about the poor prognosis, the parents opted for medical termination. At 20 weeks, mifepristone 200 mg was administered orally, followed by misoprostol 400 mcg per vaginally every 4 h. The twins were delivered after two doses. Standard dosing was employed considering her primigravida status and gestational age. The patient remained hemodynamically stable post procedure, experiencing mild abdominal pain for 1 day without fever, chills, or other complications.

4. Outcome and Follow‐Up

4.1. External Characteristics

External examination revealed male dicephalic parapagus dibrachius tripus conjoined twins, with two heads, one trunk, two upper limbs, and three lower limbs. The twins weighed 600 g, and the placenta weighed 1000 g (Figure 1).

4.2. Head, Facial Aspects, Neck, and Torso

Both heads had normal facial features. The right head was larger (head circumference: 18 cm vs. 16 cm). A widened thorax and abdomen were noted, with a single umbilical cord with three vessels. A third lower limb was observed dorsally (Figure 1).

4.3. Extremities, Genital, and Anal Areas

Upper and lower limbs were normal except for the middle lower limb, which originated from the lumbosacral region and had eight toes, including one enlarged toe on the mid‐dorsum. A single penis, one scrotum with undescended testicles, and an imperforate anus were noted (Figure 1).

4.4. Babygram Findings

The babygram showed two developed craniums, two spines, and two rib cages, though skeletal superimposition limited visualization. The pelvic bones were visible but not differentiated. The upper and lower limbs had normal bone structures (Figure 2).

FIGURE 2.

Babygram of dicephalic parapagus twins showing normally developed cranium in both twins with two separate vertebral columns, two thoracic cages, two upper and three lower extremities with normally developed upper and lower segment bones, and fusion of the lower body at the level of the pelvis.

An autopsy was not performed due to the parents' refusal, limiting insights into the internal anatomy of the shared organs. However, the parents consented to specimen preservation at our institute for educational use.

5. Discussion

Conjoined twins result from anomalies in monozygotic, monoamniotic twinning. Two main theories explain their development: the fission theory, which proposes incomplete division of the inner cell mass between days 13 and 15 post‐fertilization, and the fusion theory, which suggests that embryos initially develop independently but later fuse during the early embryonic period [1]. This theory is supported by evidence showing that conjoined embryos are typically united at sites where the surface ectoderm is absent or preprogrammed to undergo fusion or disruption [6]. Some researchers argue that all conjoined twins, except for the parapagus type, arise through the fusion process [3, 7].

The incidence of congenital anomalies is high in conjoined twins, possibly due to defective division or abnormal embryonic fusion, indicating a shared pathogenesis between conjoining and malformations [8]. Classification is based on the site of union, with the suffix “‐pagus” denoting fixed parts. Common types include thoracopagus, omphalopagus, ischiopagus, and parapagus variants such as dicephalus, where a single trunk bears two heads. Thoracopagus is the most common (42%), followed by parapagus dicephalus (11.5%) [1]. Although conjoined twins predominantly occur in females, parapagus variants show a higher incidence in males [1, 7].

In our case, we observed a rare parapagus dicephalus configuration with two heads, two upper limbs, and three lower limbs, differing from the usual form which has four limbs [9]. Though a babygram showed two thoracic rib cages, only one heart was detected by prenatal ultrasonography and on obstetric auscultation. Limitations in imaging—absence of fetal echocardiography, CT, and MRI—hindered detailed assessment of internal anatomy and organ sharing. Furthermore, the lack of autopsy prevented confirmation of visceral anatomy. These factors represent the limitations of our study. However, the strength of our case is that external morphological assessment was conducted on the day of delivery before preservation in formaldehyde solution, thus avoiding formaldehyde‐induced tissue alterations.

Real‐time ultrasound has been the most reliable method for diagnosing conjoined twins and identifying associated anomalies during pregnancy [6]. High‐resolution ultrasonography allows detection of conjoined twins as early as the 8th week of gestation, enabling early counseling and management planning [8].

Once diagnosed, early second‐trimester counseling helps families understand prognosis and consider termination, especially in cases with poor survival like dicephalus parapagus twins, who are often stillborn or die shortly after birth due to complex cardiopulmonary anomalies [9, 10, 11, 12, 13]. Separation is rarely feasible and carries ethical, surgical, and quality‐of‐life concerns. Thus, early termination is often recommended to reduce maternal morbidity and psychological burden [14].

Defining the prognosis before the 24th week of gestation is crucial, as pregnancy termination via the vaginal route is still feasible at this point [6]. Induction termination may be a safe and feasible option during earlier gestations due to fetal flexibility. Pre‐procedure counseling should address potential risks, including labor dystocia, hemorrhage, and the possibility of requiring a hysterotomy or urgent dilation and evacuation (D&E) if complications arise. Clinicians must consider factors such as fetal presentation, the widest diameter of the fetuses, and the type of fusion when planning the procedure [15]. Cesarean section remains the preferred method for near‐term delivery to reduce maternal and neonatal outcomes [6].

6. Conclusion

Ultrasonography remains the gold standard for early diagnosis of conjoined twins. However, its limitation in assessing the extent of fusion and anatomy of shared visceral organs necessitates advanced diagnostic tools such as fetal echocardiography and MRI. Conjoined twins present a unique clinical challenge, particularly in resource‐limited settings. Vaginal delivery remains a feasible option for pregnancies terminated before the 24th week of gestation.

Author Contributions

Ujjwal Kumar Shah: conceptualization, resources, writing – original draft, writing – review and editing. Deepa Shah: supervision, writing – review and editing. Pappu Rijal: supervision. Khushboo Yadav: conceptualization, supervision, writing – review and editing. Manju Bista: conceptualization, supervision, writing – review and editing. Samiksha Lamichhane: investigation, supervision, writing – review and editing. Neha Shah: writing – review and editing. Sagar Mani Regmi: writing – review and editing. Vitasta Muskan: writing – review and editing.

Consent

Written informed consent was obtained from the mother for publication of this case report and accompanying images.

Conflicts of Interest

The authors declare no conflicts of interest.

Shah U. K., Shah D., Rijal P., et al., “Dicephalic Parapagus Dibrachius Tripus Conjoined Twins: A Case Report of an Unusual Twinning Phenomenon,” Clinical Case Reports 13, no. 10 (2025): e70956, 10.1002/ccr3.70956.

Data Availability Statement

The authors have nothing to report.