TRAP Sequence, Diagnosis, Treatment, and Outcome

Gordana Adamova¹, Elma A Hasanagovski²

^1,2Department of Obstetrics and Gynecology, Sante Plus Hospital, Skopje, North Macedonia

Corresponding Author: Gordana Adamova, Department of Obstetrics and Gynecology, Sante Plus Hospital, Skopje, North Macedonia, Phone: +38978266087, e-mail: gadamova@hotmail.com

Received: 17 July 2023; Accepted: 30 October 2023; Published on: 28 December 2023

ABSTRACT

Twin reversed arterial perfusion (TRAP), a rare condition (0.3:10,000) that occurs in monochorionic twin pregnancies, with the coexistence of a normal ”pump twin” and an acardiac twin. The acardiac twin is parasitic, using an anomalous reversal of umbilical arterial flow. This anastomosis occurs in the 3rd–4th week of gestation, and the acardiac twin puts the pump fetus at risk of high-output cardiac failure. The pump twin has a mortality rate of up to 55%. Antenatal ultrasound recognition in the first trimester Doppler confirmation of the diagnosis of TRAP sequence in twin pregnancies aids in proper prenatal diagnosis.

Presented is a 26-year-old woman, gravida para, who came to our hospital at 19th gestational week (GW). The first ultrasound showed a twin monochorionic/diamniotic pregnancy, with one normally developed fetus and an atypical mass without a heart. The patient was previously monitored elsewhere, but TRAP syndrome wasn’t identified. We followed her until the 26th week, and she was later sent to a tertiary center for further conservative treatment in the absence of operative treatment in our country. The patient gave birth via C-section in the 32nd gestation week. The normal twin was born in good condition and was sent home after a few weeks.

How to cite this article: Adamova G, Hasanagovski EA. TRAP Sequence, Diagnosis, Treatment, and Outcome. Donald School J Ultrasound Obstet Gynecol 2023;17(4):360–363.

Source of support: Nil

Conflict of interest: Dr Gordana Adamova1 is associated as the International Editorial Board member of this journal and this manuscript was subjected to this journal’s standard review procedures, with this peer review handled independently of this editorial board member and her research group.

Keywords: Acardiacus, Case report, Twin reversed arterial perfusion sequence, Ultrasound

INTRODUCTION

Twin reversed arterial perfusion (TRAP) sequence/acardiac twinning is a rare anomaly. It occurs in monozygotic monochorionic twins with an incidence of 1:35,000 pregnancies overall.¹ In the TRAP sequence, the normal twin donates blood to the abnormal twin through its umbilical arteries via vascular anastomoses in the placenta. So, the acardiac twin is a parasite compared to the normal twin. The anomalous twin appears as a heterogeneous mass, simulating a teratoma or even intrauterine fetal demise. The pump twin has a mortality rate of up to 55%.²^,³ Early diagnosis by ultrasound and Doppler examination of the umbilical arteries of the two fetuses is necessary for appropriate antenatal management and treatment planning.²^,⁴

CASE DESCRIPTION

A 26-year-old woman, G1P0A0, came to our hospital for an examination at 19 weeks gestation because the doctors told her that something was wrong with the second twin. We determined that it was a monochorionic, diamniotic twin pregnancy with one normal fetus of 19 weeks gestational age. The second fetus was oval in shape; the whole body was incorporated into one large mass. An incompletely formed skeleton could only be seen in the lumbosacral part. It had no head, upper limbs, heart, or thoracic structures, an abdomen that was not clearly separated from the thoracal part, and no intraabdominal organs. On the first ultrasound examination, one cystic formation was seen in the abdomen, hyperechoic, with flat edges. There were two developed lower limbs, with short bones and foot deformity (Fig. 1). A large placental mass was visible anteriorly and to the left side of the uterus (Fig. 2).

Fig. 1: Foot deformity

Fig. 2: Large placental mass

On color Doppler, the umbilical artery in the abnormal fetus showed flow reversal on the spectral plot. The umbilical cord of the abnormal fetus was short and had only one umbilical artery. This appearance is typical of a TRAP sequence with an acardiac parasitic twin.

We performed regular controls every 2 weeks. In the 21st week, the normal fetus was screened for anomalies. No deviations from normal anatomy were found. The amount of amniotic fluid was normal. The heart had regular dimensions and anatomy. The second fetus was larger than the previous measurement.

In the 23rd week, the growth of the pump twin was also adequate for the week (Fig. 3), and the second fetus was significantly larger than the previous examination, that is, 140 × 100 mm (Fig. 4).

Fig. 3: The growth of the pump twin at 23rd week

Fig. 4: The parasitic fetus with dimensions 140 × 100 mm and cystic formation at 23rd GW

Biometrics at 25 weeks of a healthy fetus was adequate (Figs 5A and B), the parasitic fetus had dimensions of 167 × 122.4 mm (Fig. 6), and the femur was 37.8 mm/gestational age was 22 weeks and 1 day, with a percentile of <2.3% (Fig. 7). For the first time, a new second cystic formation is shown. In that week, we noticed low-grade regurgitation on the mitral valve in the heart of a healthy pump twin.

Fig. 5A and B: Parasitic fetus at the 25th GW had dimensions of 167 × 122.4 mm; (A) Acardiac twin with 2D with the appearance of two cysts; (B) The same section of acardiac twin with TUI

Fig. 6: Short femur of the acardiac twin at 25th gestation week

Fig. 7: Parasitic twin after delivery

In the 26th week, we referred the patient to a specialist in the field of fetal medicine and intrauterine fetal surgery in a specialized institution for fetal medicine and intrauterine fetal surgery, for a second opinion or eventual emergency laser coagulation of the acardiac twin’s umbilical cord, where it was determined that it was not possible to perform laser coagulation due to the gestational week (GW), short cervix, and the risk of premature birth. After such a finding, we referred the patient to a tertiary center for further treatment.

The further treatment was done conservatively, and the patient gave birth in the 30 + 3rd gestation week via a C-section. The normal twin was 1180 gm, 36 cm, with an Apgar score of 5/6/6. The parasitic was 1990 gm/25 cm and is shown in Figure 7.

DISCUSSION

It is an easy mistake to misdiagnose TRAP, especially because it is rare to see this kind of syndrome. TRAP should be appropriately diagnosed and treated early to avoid complications of the pump twin. The diagnosis should be made before the end of the first trimester, and because of the development of ultrasound machines, TRAP syndrome can be diagnosed as early as the 11th week of gestation.³ The characteristic ultrasound sign that helps diagnose TRAP syndrome is monozygotic twins with one morphologically normal fetus and one structurally highly abnormal fetus without a heart. Doppler imaging of the umbilical artery shows reverse arterial blood flow to the acardiac twin.³^,⁵^,⁶ Our case was diagnosed late due to being previously misdiagnosed.

The indications for prenatal invasive treatment include polyhydramnios, cardiac dysfunction, hydrops of the pump twin, or a relatively large weight of the acardiac twin.⁷

Prenatal treatment involves occlusion of blood flow to the acardiac twin by endoscopic (fetoscopic) ligation or laser coagulation of the umbilical cord, bipolar cord cauterization, or intrafetal radiofrequency ablation.⁸^,¹¹

Each of these procedures involves risks for both mother and baby, including preterm labor and delivery; overall success rates are high. The patients should be informed of the survival rate associated with each technique.

CONCLUSION

An accurate diagnosis and well-timed treatment will prevent damage to a healthy fetus and the possibility of extending the pregnancy, which is in the interest of a healthy fetus.

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