TRAP, acardiac, outcome

Dieter Grab, MD Volker Schneider, MD Jorg Keckstein, MD Rainer Terinde, MD

Address correspondence to: Dieter Grab, MD, Department of Obstetrics and Gynecology, University of Ulm, Prittwitzstr.ÿ43, 7900 Ulm, Germany. Ph: 49-731-179-4140; Fax: 49-731-179-2420


The acardiac twin gestation represents a syndrome characterized by vascular anastomoses in combination with partial or complete lack of cardiac development in one of the twins1. The preferred term for the syndrome is now twin reversed arterial perfusion (TRAP) sequence. The incidence of this disease is approximately one in 35,000 pregnancies1. Commonly, congestive heart failure of the pump twin, hydramnios and preterm labor occur, resulting generally in poor outcome. In the following, we report four cases of acardiac twinning illustrating the wide spectrum of possible outcomes in this disease and the corresponding management.

Case # 1

A 20-year-old G1P0 presented in the 20th week of a twin gestation. One fetus appeared sonographically normal; the other fetus was growth retarded with no cerebral and cardiac structures recognizable. Chromosomal analysis of amniotic cells showed two normal female patterns. There was increasing hydramnios and beginning cardiac insufficiency of the normal fetus in the 24th week. Therefore, it was decided to occlude the anastomosing vessels. After unsuccessful instillation of a glucose solution into the Wharton"s jelly of the acardiac fetus, a sonographic-guided cord puncture was performed and the umbilical vein of the acardius was occluded by fibrin clot. There was immediate complete venous occlusion. Unfortunately, 12 hours later intrauterine fetal death occurred also in the second twin. The postmortem examination showed that both umbilical cords had three vessels, as sonographically seen. The umbilical vein of the acardiac fetus was completely occluded by fibrin. There was also occlusion of the umbilical vein in the second fetus by a fibrin clot over a distance of approximately 1 cm, following the transmission of fibrin through a veno-venous anastomosis between the two cords.

Case # 2

A 23-year-old G1P0 was transferred in the 15th week of a twin pregnancy because of hydrops of one of the twins. This hydropic twin showed no cardiac contractions; however, active movements of the lower extremity were noted. Sonographically, there was rapid increase in the amount of amniotic fluid with persistent signs of vitality of the acardiac twin. The healthy twin developed normally. Because of increasing abdominal girth of the mother, an occlusion of the vascular connection of the two fetuses was considered. Doppler examination showed, however, that both umbilical cords had only two vessels and the vascular systems were interconnected. The pulsation of the umbilical artery of the normal fetus was transmitted into the vascular system of the acardiac fetus (fig. 1).


Fig 1: Flow profile of the central vessel in the acardiac twin of case 2. The pulsation profile (bottom) indicates a direct connection between the two vascular systems. Location of the Doppler probe in the acardiac twin (top).

Accordingly, occlusion of the vascular anastomosis was therefore ruled out.

In the 24th week, the patient was admitted following the development of preterm labor, non-responsive to maximal tocolysis. Therefore, a cesarean section was performed in the 24th week with development of a depressed preterm infant of 910g, Apgar 1/6/8, pH 7.24 and a severely hydropic acardiac twin of 2500g. Despite postpartal ventilation and surfactant treatment, the normal twin died three weeks postpartum with the signs of cerebral hemorrhage, cardiomyopathy, acute renal failure with anuria, progressive respiratory insufficiency with bronchopulmonary dysplasia and pneumothorax bilaterally.

Postmortem examination showed two vessels in both cords with an anastomosing vessel between both cords running across the surface of the placenta. The acardiac-acephalic twin (2500g) showed rudimentary development of the lower half of the body with only three digits on each foot. The upper portion of the body consisted of a mass of undefined connective tissue with extreme edema, and no cardiac or lung development was present.

Case # 3

A 26-year-old G2P1 was initially seen in the 16th week of a twin gestation. An acardiac-acranial twin was present. There were spontaneous movements of the lower extremities. Chromosomal analysis of amniotic fluid showed two normal females. Several ultrasonographic examinations showed lack of growth of the malformed twin but appropriate growth of the normal twin.Spontaneous labor developed at 40 weeks and a normal female, 3270g, with Apgar 9/10/10, was delivered. The acardiac twin was approximately 10 cm long and was spontaneously delivered out of a second amniotic cavity.

Pathologic findings

The female acardiac acephalic twin (31g, 10 cm) showed no heart or lung development; liver, intestine, and urogenital tract appeared normal. Spleen, pancreas and stomach were absent. The placenta was monochorionic diamniotic, and the two umbilical cords were interconnected by a direct anastomosis.

Case # 4

A 35-year-old G2P1 presented with an acardiac twin gestation at 16 weeks. At the 19th week, spina bifida and hydrocephalus were detected in the pump twin. At this point the couple elected to terminate the pregnancy with prostaglandin induction. The prenatal diagnoses were confirmed (fig. 2).


Fig. 2: Case 4, 19 weeks twin pregnancy after prostaglandin abortion. Note the spina bifida and the hydrocephalus of the pump twin. Only the lower extremities are well defined in the acardiac twin.


Weight ratios

The twin reversed-arterial-perfusion sequence (TRAP-sequence) carries a poor prognosis with a mortality rate of approximately 50%2,3. The prognosis is directly related to the respective weight of recipient to pump twin. The higher the weight of the recipient twin the more likely is the development of cardiac insufficiency in the pump twin3. Management should be guided by the mortality risk of conservative treatment: if the acardiac twin is considerably smaller than the pump twin, a normal delivery at term can be expected. This situation is illustrated by our caseÿ3. Although the acardiac twin showed vitality of the lower extremity, there were no hemodynamic complications of the pump twin based on the small weight of the acardiac twin. In contrast, the extreme hydrops of the recipient twin in case 2 required an increasing cardiac output by the pump twin.

Vessel occlusion

Considering the failure to occlude the umbilical vein of the acardiac twin by fibrin in case 1, this therapeutic management was discarded for case 2 after vascular anastomoses had been demonstrated. Ultrasonography, as well as Doppler sonography, showed the presence of only two vessels in both umbilical cords with direct communication of the circulation. An occlusion of the vessels to the acardiac twin would have induced an acute increase in the pressure gradient with the concomitant risk of severe bradycardia. Although the pump twin did not show any signs of cardic insufficiency, death occurred due to dilative cardiomyopathy.

Use of digoxine

Possibly, an intrauterine prophylactic digoxine treatment could have improved the outcome. Simpson et al.4 report on a twin pregnancy with an acardiac and normal fetus of about even size. There were sonographic signs of cardiac insufficiency which disappeared completely after treatment with digoxine over six weeks. The vaginally delivered normal twin survived. Likewise, the fetofetal twin transfusion syndrome with cardiac insufficiency of one of the twins has also been treated successfully by prenatal digoxine application5. Treatment was initiated after the sonographic diagnosis of fetal cardiac insufficiency.

Associated anomalies in the pump twin

The occurrence of the TRAP-sequence together with a neural tube closure defect of the donor twin (case 4) has not yet been reported. To date, all published cases report a morphologically and chromosomally normal donor twin. This case illustrates the necessity of a careful search for malformations of the second twin in order to avoid unnecessary invasive treatment modalities.


Based on our own experience and the published recommendations of others1,4,6 we suggest the following strategies for management of these cases: after exclusion of chromosomal aberrations and malformations of the pump twin, a close sonographic follow-up is initiated. If the estimated weight of the acardiac twin is less than one fourth of the pump twin, the prognosis is excellent without further therapy. Although an estimated fetal weight is not possible in acardiac fetuses (since the BPD is not available and the femur may be severely shortened), one can derive a rough estimate of the weight by comparing the ratio of the abdominal perimeter of the acardiac and pump twin, or apply the formula of the prolated ellipsoid (length of acardiac times abdominal diameters divided by two).

In the majority of cases, spontaneous delivery will occur at term3. The risk of cardiac insufficiency of the pump twin increases parallel to the relation in weight of recipient to pump twin. The risk of congestive heart failure increases to 94%, with the acardiac twin being more than half of the size of the pump twin3. In these cases a prophylactic intrauterine treatment with digoxine even before the manifestation of cardiac insufficiency is recommended. If hydramnios or signs of fetal cardiac insufficiency such as ascites, pericardial effusion, cardiomegaly or hepatomegaly occur, intrauterine treatment such as repeated fluid aspirations, occlusion of the acardiac vascular system by transabdominal puncture of the umbilical cord and instillation of fibrin, fetoscopic clipping or laser coagulation of anastomoses become necessary. Preterm selective removal of the acardiac twin by section parva may become necessary 1,6,7. Among these modalities, the transabdominal puncture of the umbilical cord is the method of first choice. A preoperative exact evaluation of the vascular flow including Doppler sonography is, however, mandatory.


1. Romero R, Pilu G, Jeanty P et al: Prenatal diagnosis of congenital anomalies. East Norwalk, Conn.: Appleton & Lange, 1987 pp. 409-411.

2. Van Allen MI, Smith DW, Shepard TH: Twin reversed arterial perfusion (TRAP) sequence: a study of 14 twin pregnancies with acardius. Semin Perinatol 7:285-293,1983.

3. Moore RT, Gale S, Benirschke K: Perinatal outcome of forty-nine pregnancies complicated by acardiac twinning. Am J Obstet Gynecol 63:907-912, 1990.

4. Simpson PC, Trudinger BJ, Walker A, et al: The intrauterine treatment of fetal cardiac failure in a twin pregnancy with an acardiac, acephalic monster. Am J Obstet Gynecol 147:842-844,1983.

5. De Lia JE, Emery MG, Sheafor A, Jennison TA: Twin transfusion syndrome: successful in utero treatment with digoxin. Int J Gynecol Obstet 23:197-201,1985.

6. Platt LD, DeVore GR, Bieniarz A, et al: Antenatal diagnosis of acephalus acardia: a proposed management scheme. Am J Obstet Gynecol 146:857-858,1983.

7. Robi GF, Payne GG, Morgan, MA: Selective delivery of an acardiac acephalic twin. N Engl J Med 320: 512-513,1989.

8. Pretorius DH, Leopold GR, Moore TR, et al: Acardiac twin: report of Doppler sonography J Ultrasound Med 7:413-416,1988.

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