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.
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.
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.