The Case of the Vampire Baby Case Report: Twin Reversed Arterial Perfusion Sequence

Abstract

Twin reversed arterial perfusion (TRAP) sequence is a rare divergence of monozygotic monochorionic twin gestations resulting in an acardiac twin receiving its blood supply from an otherwise structurally normal twin via placental vascular anastomoses. If not managed, this unusual complication poses increased risks of heart failure in the viable twin, polyhydramnios, and parental mortality. This case report follows a primigravida second-trimester TRAP pregnancy, highlighting the necessity of serial observations and timely management to lessen morbidity and mortality.

Keywords: TRAP sequence; Twin gestations; Placental arterial anastomoses

Abbreviations

TRAP: Twin Reversed Arterial Perfusion; ED: Emergency Department; ER: Emergency Room; HCG: Human Chorionic Gonadotropin

Case Presentation

A 29-year-old gravida 0, otherwise healthy, African American female presented to the ED with a 3-day history of worsening lower abdominal pain. The patient described the pain as sharp, severe, right lower quadrant pain radiating to the lower back. The patient denied nausea, vomiting, vaginal bleeding, dysuria, hematuria, change in bowels, and fever. She was stable with normal vital signs at time of presentation. Her last menstrual period was 2 months prior to the ED visit. A positive urine pregnancy test was obtained with subsequent quantitative beta-HCG. The transvaginal ultrasound revealed a twin gestation of approximately 7 weeks. Though twin pregnancy was confirmed, because there was no appreciable heartbeat noted from either embryo at the time, the attending ER physician recommended dilatation and curettage. The patient declined. She was discharged and instructed to follow-up with her obstetrician.

During the initial prenatal visit, a heartbeat was discovered in one twin, the other was termed a “vanishing twin.” The mother was advised that this twin would not develop further and would likely be “reabsorbed,” by the surviving twin. At the 17-week fetal anatomy ultrasound, a monochorionic-diamniotic gestation was confirmed; however, perfusion to the nonviable twin was detected. Furthermore, growth of the abnormal twin was notable in comparison to prior prenatal and ED ultrasounds. Though the anomalous twin was growing, it was amorphous with no distinct limbs or organs. Subsequently, the patient was referred to maternal fetal medicine and the diagnosis of twin reversed arterial perfusion sequence-acardius amorphous, was established.

The remainder of the pregnancy included genetic counseling and weekly visits to specialists at a regional children’s hospital. Each visit consisted of a detailed ultrasound with measurements of crownrump length, biparietal diameter, femur length, and abdominal circumference of the viable fetus; echocardiogram; amniotic fluid index; measurements of blood flow to the acardiac twin, donor twin, and placenta; as well as documentation of the growth of the viable twin relative to the nonviable twin. At the initial visit, the ratio of recipient to donor twin growth was 0.30; this increased over the course of weekly ultrasounds up until delivery at 38 weeks with a final ratio of 0.41. A ratio greater than 0.70 signaled stress to the viable twin’s heart and would have necessitated intervention.

Antenatal corticosteroids were administered at 34 weeks to aid fetal lung maturity and labor was induced at 38 weeks with a Foley balloon catheter and Oxytocin drip. An African American-Hispanic boy was delivered vaginally, weighing 2466.4 grams with Apgar scores of 8 and 9 at one and five minutes, respectively. After failed attempts at vaginal delivery of the abnormal twin, the mother was taken to the operating room for dilation and evacuation. It was essentially a mass, weighing 907.2 grams with no identifiable head or extremities. The mother suffered a third-degree vaginal tear and was catheterized for three days to prevent urinary retention. The remaining hospital stay was uneventful and both mother and baby were discharged four days postpartum.

Discussion

TRAP remains an uncommon anomaly exclusive to monochorionic multifetal gestations with an incidence of 1 in 9,500- 11,000 pregnancies and 2.6% of monochorionic twin pregnancies [1-2]. Aside from these statistical findings, there are no known risk factors.

Two theories explain this phenomenon, dysmorphogenesis versus presence of arterio-arterial anastomosis [2-3]. The less popular theory, dysmorphogenesis, defines the underlying pathology as a defect in early organogenesis, resulting in a fatal malformed cardiac system [3]. Though arterial anastomosis contributes to the reversed blood flow, it is not responsible for the acardia. The arterio-arterial anastomosis concept describes a reversed umbilical artery blood flow as the principal cause of acardia. In this model, anastomosis causes deoxygenated arterial blood to flow from the donor to the recipient twin [3]. Unfortunately, circumventing the placenta results in a lack of proper perfusion for vital organ development, leading to the recipient twin appearing as a heterogeneous mass rather than a normally developing fetus. The acardiac twin essentially becomes a parasite, putting the surviving twin in danger of high-output cardiac failure, polyhydramnios, preterm birth, structural defects, and hydrops fetalis. Twin reversed arterial perfusion holds a perinatal mortality rate of 55% if not treated [4].

The artery-to-artery connection serves as the underlying cause of TRAP sequence. Arterial anastomosis and reverse flow of deoxygenated blood lead to stunted growth of the recipient twin. While the recipient twin mainly receives oxygen-poor blood, there is slightly more nutrient-rich blood flowing to the common iliac arteries and abdominal aorta that typically allow for growth of lower extremities, abdominal, and reproductive organs. This unequal vascular perfusion explains the different morphologies of TRAP [2].

The four types of acardia are classified based on presence or absence of various limbs and organs (Table 1) [5]. The most common type, acardius acephalus is the absence of a head, upper extremities, and trunk but maintenance of lower limbs, genitalia, and abdominal organs. In acardius anceps, the most developed type, facial features and cranial structures are present but incomplete along with rudimentary limbs and organs.

  

    
Acardius    Acephalus
    
•   Absence    of head, upper extremities, and trunk. Maintenance of lower limbs, genitalia,    and abdominal organs
  
  

    
•    Most    common type
  
  

    
Acardius
      
Anceps
    
•    Present,    but incomplete facial features and cranial structures. Rudimentary limbs and    organs
  
  

    
•     Most    developed type
  
  

    
Acardius    Amorphous
    
•     Heterogenous    mass. No head, extremities, or organs
  
  

    
•     Least    developed type
  
  

    
Acardius
      
Acormus
    
•     Head    is the only formed structure, no limbs and organs
  
  

    
•     Least    common type
  
  

    
Due    to the sensitive nature of this case report, the patient declined use of    ultrasound imaging or photographs for publication. 
      
 
  

Table 1:  4 Types of TRAP morphologies.