- What Is TRAP?
In TRAP sequence, one twin develops normally (pump twin) while the other develops without a functioning heart (acardiac twin), cardiac system and other structures that would allow this twin to develop and thrive.
The twins are joined by a large blood vessel between their umbilical cords that passes through the placenta. The acardiac twin receives all of its blood from the pump twin, which causes the pump twin’s heart to work harder than it should.
TRAP sequence is a condition where blood flow to and from the acardiac twin is opposite of the way blood is normally supplied. Thus, the reason for the term “reversed arterial perfusion.”
- Prenatal Diagnosis of TRAP
At Fetal Care Center Dallas, our physicians are experienced in the diagnosis and treatment of expectant mothers with TRAP sequence. Detection of TRAP sequence may occur during a routine prenatal ultrasound showing a single placenta containing two fetuses.
Ultrasound may also show excess amniotic fluid surrounding the twins, who often share the same amniotic sac. If you receive a diagnosis of TRAP sequence, our physicians will work closely with your obstetrician in your care and confirm the diagnosis using fetal echocardiography, a specialized ultrasound of the heart and blood vessels that can assess blood flow between the twins and confirms the presence of the condition.
Close observation by ultrasound/fetal echocardiography will be essential throughout your pregnancy so we may monitor the heart health of the pump twin and the size of the acardiac twin for signs of possible intervention.
If signs of heart failure appear in the pump twin early in your pregnancy, physicians at Fetal Care Center Dallas will discuss treatment options and outcomes with you.
- How We Treat Babies with TRAP
While all TRAP sequence pregnancies require careful monitoring, not all require treatment. In treated cases, our goal is to preserve the life of your healthy twin. If the pregnancy has progressed far enough along, delivery of the healthy twin may be recommended without the need for additional treatment.
If the health risk for the pump twin becomes high enough early in pregnancy, other prenatal treatments may be recommended to stop the extra pumping between the twins.
Our fetal surgeon may perform radiofrequency ablation (RFA) using highly specialized equipment and techniques within the womb to block the flow of blood to the acardiac twin. This process allows the healthy twin to survive and develop as normally as possible.
With a spinal anesthesia administered to the mother and ultrasound guidance, the physician performs radiofrequency ablation using a thin needle-like device placed through the mother’s abdomen and uterus into the abnormal twin’s umbilical cord.
Heat energy is then applied to stop the blood flow to the cord. RFA has been shown to be a successful treatment method with a high survival rate for the normal twin when delivered after 35 weeks into the pregnancy.
- Focused on the Most Complex of Pregnancies
The maternal fetal medicine physicians at Fetal Care Center Dallas care for a high volume of monochorionic twin pregnancies each year. This experience helps to continuously expand our understanding of these complex pregnancies and our ability to differentiate between TRAP sequence and other conditions such as intrauterine growth restriction or twin-to-twin transfusion syndrome.
- Long-Term Outlook for Twins With Trap Sequence
For twins found to be at risk of heart failure, there is a high risk of pregnancy loss. With treatment, however, survival rate is very high and the average delivery occurs at around 35 weeks. For those pregnancies that are at low risk for complications, outcomes are even better.
For Healthcare Providers
- TRAP: Introduction
Twin reversed arterial perfusion (TRAP) sequence, also known as acardia, is a rare anomaly unique to multiple gestation in which one twin has an absent, rudimentary, or nonfunctioning heart. Schatz (1898) classified acardia into two main groups: hemiacardius (imperfectly formed heart) and holoacardius (absence of heart). Das (1902) subdivided acardia into four groups: acardius acephalus, acardius amorphus or anideus, acardius acormus, and acardius anceps or paracephalus (Table 120-1). Simonds and Gowen (1925) added a further subgroup: acardius myelacephalus.
Contemporary authors have considered these classifications meaningless because the pathogenesis is probably similar for all cases (Benirschke and Kim 1973; Van Allen et al. 1983). Van Allen et al. recommended twin reversed arterial perfusion sequence to describe all acardiac fetuses. The TRAP sequence denotes a common pathophysiology for all forms and leads to an explanation of how a gradation of abnormalities can be produced (Van Allen et al. 1983). The fundamental requirement for the TRAP sequence is the development of arterial-to-arterial vascular anastomoses between the umbilical arteries of twins early in embryogenesis. The importance of vascular arterial anastomosis as the pathophysiology for acardia was first elucidated in 1879 by Ahlfeld. The embryo with the hemodynamic advantage becomes the pump twin. The pump twin retrogradely perfuses the other twin with deoxygenated blood along the umbilical artery/arteries to the iliac artery/arteries to the abdominal aorta. The lower limbs and abdominal organs supplied by the iliac arteries and abdominal aorta preferentially receive a better blood supply and usually develop better than the upper part of the body (Van Allen et al. 1983). TRAP occurs in monochorionic pregnancies, and previous theories of polar body fertilization to explain acardius in sex discordant twins have been discounted (Bieber et al. 1981; Fisk et al. 1996). In addition, the TRAP sequence is more common in monozygotic triplets than in monozygotic twins (James 1977; Healey 1994). Some authors have suggested a slight female preponderance in acardiac twins while other studies have not supported this idea (Healy 1994, James 1977).
The members of a TRAP sequence are known as the perfused twin and the pump twin. The perfused twin in a TRAP sequence is an example of the impact of vascular disruption on morphogenesis. Multisystem malformations, as well as unusual body form, are found in the perfused twin. Figure 120-1 illustrates the gradation of loss of normal body form ranging from an amorphous appearance to an individual with more severe abnormalities found in the upper part of the body. The malformations found in cases of acardia include growth abnormalities, partial or complete absence of the cranial vault, anencephaly, holoprosencephaly, absent or rudimentary facial features, absent or rudimentary upper and/or lower limbs, absent lungs and heart, gastrointestinal atresia, omphalocele, gastroschisis, and absent liver, pancreas, spleen, and kidneys (Van Allen et al. 1983). Of 33 acardiac fetuses with a known karyotype, 11 (33%) were abnormal (Healey 1994). The karyotypic abnormalities included monosomy, trisomy, deletions, mosaicism, and polyploidy. The pattern of structural abnormalities found in the perfused twins with abnormal karyotypes is not appreciably different from those with normal karyotypes (Van Allen et al. 1983). Van Allen et al. suggested that the abnormal karyotype is not responsible for the malformation complex, but rather that it contributes to the discordant development between twins, increasing the likelihood of reversal of arterial blood flow if an anastomosis occurs.
The presence of an acardiac twin requires a “pump” twin to provide circulation for itself as well as its acardiac co-twin. In many cases the acardiac twin is almost equal in size to the normal twin (Figure 120-2). The pump twin is usually morphologically and genetically normal. In a review of 34 pump fetuses with a known karyotype, 3 (8.8%) were abnormal as a result of trisomy (Healy 1994). The pump twin may show evidence of the physiologic consequence of fetal cardiac overload and congestive heart failure with hepatosplenomegaly. The principal perinatal problems associated with acardiac twinning are pump twin congestive heart failure, polyhydramnios, and preterm delivery (Moore et al. 1990).
The reported fetal/neonatal mortality in the pump twin is substantial ranging from 50-75% (Gillim and Hendricks 1953; Napolitani and Schreiber 1960; Van Allen et al. 1984; Moore et al. 1990; Sogaard 1999). One factor thought to be contributing to the high perinatal mortality rate is the increased cardiac demands placed on the pump twin to perfuse the acardiac twin (Sullivan et al. 2003).
Premature delivery is another important factor determining the prognosis for the pump twin (Figure 120-2) (Healey 1994; Moore et al. 1990; Van Allen et al. 1983). In one study where approximately 55% of acardiac pregnancies resulted in fetal or neonatal death, approximately one quarter of the pregnancies delivered after 36 weeks. Preterm delivery and the attendant long-term morbidities complicated the remaining quarter (Moore et al. 1990).
- Incidence of TRAP
The incidence of the TRAP sequence is estimated as 1% of monozygotic twins, with birth estimates ranging from 1/35,000 to 1/50,000 births (D’Alton and Simpson 1995, Gillim and Hendricks 1953, Napolitani and Schreiber 1960). Acardia was observed in 1 of 606 twin pregnancies, and the rate of twins was calculated at 1 in 86.5 births in the United States (Gillim and Hendricks 1953). Van Allen et al. (1983) have suggested these figures to be a gross underestimate of the true frequency of the TRAP sequence because most cases go unrecognized due to early pregnancy loss. In contrast, an analysis of data from the Eurocat Network (European Registration of Congenital Anomalies and Twins) gave a prevalence of acardia of 0.064 in 10,000 births, which is much lower than were previous estimates in the literature (Haring et al. 1993).
- Sonographic Findings
Antenatal diagnoses of the TRAP sequence have been reported in the literature since 1980. Ultrasonographic features useful in the diagnosis of acardia include absence of normal cardiac structure and cardiac movement and variable structural abnormalities. Common structural abnormalities identified in the acardiac fetus include anencephaly, omphalocele, and absence of upper limbs. Most cases have edematous soft tissue, and large cystic hygroma–like spaces are commonly identified in the skin (Mack et al. 1982).
The placentation is most commonly monochorionic diamniotic (74%), in which a thin membrane will be seen dividing the sac of the acardiac fetus from the pump fetus (Healey 1994). Monoamnionicity is present in approximately 24% of cases (Healey 1994). In exceptional cases, dichorionicity may be diagnosed (Healey 1994). Polyhydramnios is common as are abnormalities in the umbilical cord or in its insertion (Dashe et al. 2001). The umbilical cord will demonstrate a single umbilical artery in approximately two thirds of cases, and in one third the number of cord vessels will be normal (Healey 1994). A velamentous insertion of the cord or a conjoined cord insertion may be present (Dashe et al. 2001).
Measurement of the acardiac twin should be performed, because the ratio of the weight of the acardiac twin to that of the pump twin is useful to predict pregnancy outcome. Because of the structural abnormalities, the biometric parameters of biparietal diameter, abdominal circumference, and femur length may not be available or reliable in an acardiac fetus. This problem of the antenatal determination of the acardiac twin’s weight has been addressed by Moore et al. (1990). The dimensions and weights of 23 acardiac twins were used for the analysis. A second-order regression equation (weight [g] = –1.66 × length + 1.21 × length2) was computed and was predictive of acardiac weight with the use of its longest linear measurement (r = .79; P < 0.001; SEE = 326 g). When the actual and equation-predicted weights were compared, the mean error (±SE) in prediction was 240 ± 156 g. Careful Doppler examination of the acardiac fetus may also demonstrate reversal of flow in the umbilical artery of the acardiac fetus, with flow going from the placenta toward the acardiac fetus (Figure 120-3)(Benson et al. 1989; Malone and D’Alton 2000).
The pump twin should have a detailed structural survey performed because trisomy has been reported in up to 9% of cases (Healey 1994) and sonographic features typical of a trisomic fetus may be identified. Fetal echocardiography is helpful in detecting early signs of in utero congestive heart failure in the pump twin. Atrial and ventricular enlargement can be an initial feature of impending cardiac decompensation and can be measured using M-mode by obtaining a transverse view through the cardiac chambers (Allan 1986; DeVore 1987). The ventricular fractional shortening capacity can also be calculated using M-mode with the formula (D – S)D × 100, where D is the diastolic and S is the systolic ventricular size. A low value is indicative of poor cardiac contractility. A pericardial effusion may be present and is a sign of congestive heart failure. Tricuspid regurgitation, demonstrated by Doppler studies of the tricuspid valve, is also a sign of congestive heart failure (Shenker et al. 1988; Silverman et al. 1985). Combined ventricular output (CVO) can be measured to determine if the pump twin is in a high output state. In TRAP sequence at a gestational age too early to determine CVO, Kinsel-Ziter et al. have demonstrated a good correlation of increased CVO with increased cardiothoracic ratio (Kinsel-Ziter et al. 2009).
Doppler studies should be performed in both the acardiac and pump twins. Verification of circulatory reversal by pulsed Doppler sonography of the acardiac twin can be documented with reversed direction of flow in the umbilical artery and vein (Benson et al. 1989; Dashe et al. 2001; Donnenfeld et al. 1991; Langlotz et al. 1991; Pretorius et al. 1988; Sherer et al. 1989). In one recent study by Dashe et al., between 1990 and 1997, Doppler studies were performed in 6 monochorionic pregnancies complicated by the TRAP sequence. Pulsatile vessels in the umbilical vessels of the acardiac and pump twins were insonated. Reversal of flow was demonstrated in all cases. Resistive index values were calculated, and the difference in resistive index between the pump and acardiac twin was evaluated. In the acardiac twins, no ratio of systolic to diastolic velocity or resistive index value was associated with a good or with a poor prognosis for the pump twin. In the pump twins, resistive index differences > 0.20 between the pump and the acardiac twins were associated with good outcomes, while resistive index differences < 0.05 were associated with poor outcomes (Dashe et al. 2001).
- Differential Diagnosis
The acardiac fetus may be mistaken for an anencephalic fetus. The sonographic features of absent trunk region in addition to increased soft tissue in the body aid in the correct diagnosis (Billah et al. 1984).
The TRAP sequence has been mistaken for intrauterine fetal death (IUFD) of one twin in a multiple gestation (Malone and D’Alton 2000). Evidence of growth in the “dead” fetus and a “twitching” noted on repeat ultrasound examination has allowed the diagnosis of an acardiac twin to be made (Cardwell 1988). In a severely macerated fetus, the skeletal and visceral forms are more differentiated, and the soft-tissue edema is less advanced than in a case of acardia (Mack et al. 1982). The use of color-flow Doppler can assist in differentiating between single IUFD in a co-twin and the TRAP sequence (Malone and D’Alton 2000). Pulsed Doppler examination has been used to demonstrate reversed flow through the umbilical artery of the acardiac twin (Pretorius et al. 1988).
- Antenatal History
The principal perinatal problems associated with acardiac twinning are pump twin congestive heart failure, maternal polyhydramnios, and preterm delivery. The antenatal diagnosis of TRAP can be made only through sonographic examination and has been reported in the literature only since 1980. Large series of acardiac twins have attempted to identify factors prognostic of favorable outcome for the pump twin (Healey 1994; Moore et al. 1990).
In the series of 49 cases reported by Moore et al. (1990), one third of fetuses were delivered before they were viable. In this study, viability was defined as delivery at or beyond 25 weeks of gestation. Of the potentially viable 33 cases, 4 (12%) ended in death of the pump twin in utero. The overall perinatal mortality was 55% and was primarily associated with prematurity (Table 120-2).
Polyydramnios was a major maternal complication, occurring in 46% of all acardiac pregnancies, and it was strongly associated with preterm labor and congestive heart failure in the pump twin. Eighty-two percent of patients with polyhydramnios experienced preterm labor requiring hospital admission and treatment, as compared with 22% of pregnancies with normal amniotic fluid (P < 0.01). Polyhydramnios was observed in 78% of pump twins with congestive heart failure as compared with 13% of those in whom congestive heart failure was not confirmed (P < 0.001). The perinatal outcome was strongly related to the ratio of the weight of the acardiac twin to that of the pump twin. The mean overall ratio of the twin weights was 52 ± 42%. The twin weight ratio was more than 70% in 25% of cases. When this characteristic was present, the incidence of preterm delivery was 90%, polyhydramnios 40%, and congestive cardiac failure in the pump twin 30%, as compared with 75%, 30%, and 10%, respectively, when the ratio was less than 70% (Moore et al. 1990).
In the series by Healey (1994), of 5 cases at Monash Medical Centre and a review of 184 case reports in the literature from 1960 to 1991, the overall perinatal mortality for the pump fetus was 35% in twins and 45% in triplets. Factors associated with a significant increase in perinatal mortality for the pump fetus included delivery before 32 weeks of gestation, the acardius anceps form of acardia, and the presence of arms, ears, larynx, trachea, pancreas, kidney, or small intestine in the acardiac fetus.
Nonetheless, a more recent study questioned the poor prognosis associated with pregnancies complicated by TRAP and explored the role of expectant management(Sullivan 2003). Ten cases of antenatally diagnosed acardiac twins delivered between 1994 and 2001 in one community were evaluated. All cases were managed expectantly. Nine women delivered a healthy pump twins. There was one neonatal death. The mean gestational age at delivery was 34.2 weeks and the mean weights of the pump and acardiac twins were 2279 g and 1372 g, respectively. The authors concluded that neonatal mortality of pump twins in antenatally diagnosed acardiac twin pregnancies may be considerably less than reported, and expectant management with close antepartum surveillance may be an option.
- Management of Pregnancy
The goal of antepartum management of a pregnancy complicated by the TRAP sequence is to maximize outcome for the structurally normal pump twin. Management of acardiac twin gestations is controversial. When the diagnosis is made, the gestational age should be documented by maternal history and standard biometric measurements of the pump fetus. The high and low risk factors for perinatal mortality in the pump fetus must be evaluated through sonographic examination. In the absence of poor prognostic features (twin weight ratio > 0.70, elevated CVO, increased C:T ration, congestive cardiac failure, polyhydramnios), expectant management with serial sonographic evaluation is reasonable (Malone and D’Alton 2000). Additional factors that place the pregnancy at high risk for perinatal mortality include features of acardius anceps demonstrating the presence of arms, ears, larynx, trachea, pancreas, renal tissue, and small intestine. Rapid growth of the acardiac twin may also be a sign of poor outcome (Brassard et al. 1999).
Features that indicate a lower risk include features of acardius amorphous with absence of arms, legs, brain, esophagus, trachea, and omphalocele (Healey 1994). Karyotyping of the pump twin should be offered because as many as 9% of pump twins have an abnormal karyotype (Healey 1994).
Various techniques have been used to interrupt the vascular communication between the twins in an effort to improve outcome of the normal pump twin. These methods have included hysterotomy with physical removal of the acardiac twin, ultrasound-guided injection of thrombogenic materials into the umbilical circulation of the acardiac twin, ligation of the umbilical cord of the acardiac twin under fetoscopic guidance, and intrafetal radiofrequency cord ablation (Ash et al. 1990; Holzgreve et al. 1994; Porreco et al. 1991; Quintero et al. 1994; Robie et al. 1989; Simpson et al. 1983; Van Allen et al. 1983; Challis 1999; Tsao 2002; Livingston et al. 2007). Steroids should be given if delivery is expected between 24 and 34 weeks of gestation (NIH Consensus Development Panel 1995). Preterm labor should be suppressed with tocolytic agents.
Delivery at a tertiary-care hospital is recommended because of the risk of preterm delivery and congestive cardiac failure in the pump twin. The vaginal route is the preferred mode of delivery. The indications for cesarean include the standard obstetric reasons. In Moore et al.’s series, abnormal presentation and fetal distress necessitated cesarean delivery in more than half of the potentially viable pregnancies.
Medical management with maternal administration of digoxin or indomethacin has been reported, but there are no significant case series on these management strategies. The use of maternal digitalization to treat cardiac failure in the pump twin was reported by Simpson et al. in 1983. Marked edema of the trunk in the normal twin was present. Fetal ascites, pleural effusion, or cardiomegaly was not demonstrated. Serial ultrasound examinations demonstrated resolution of the edema and continued normal growth of the viable fetus. Delivered at 34 weeks, the normal twin weighed 1860 g. The acardiac twin weighed 1810 g. No subsequent reports of this digoxin therapy for acardia have been reported.
Ash et al. (1990) reported the use of indomethacin in an acardiac pregnancy complicated by polyhydramnios at 21 weeks as means of reducing renal perfusion and amniotic fluid production. No evidence of cardiac failure was visualized in the pump twin. Indomethacin, 50 mg daily, was given to treat the symptomatic polyhydramnios because of the high risk of premature labor. The indomethacin was continued for 8.5 weeks. Oligohydramnios at 34 weeks prompted induction of labor, and spontaneous vaginal delivery occurred. The normal twin weighed 1865 g at birth, and the acardiac twin weighed 785 g (Ash et al. 1990).
- Fetal Intervention
Many invasive procedures have been described with the goal of interrupting the umbilical circulation of the acardiac twin. There has been controversy in the literature concerning which cases are candidates for such procedures. Previously, it was recommended that invasive procedures be performed only after heart failure has developed (Platt et al. 1983). Some have recommended surgical intervention only after medical therapy has failed (Ash et al. 1990). Others have suggested intervening before heart failure is present in the pump twin (Platt et al. 1983). Others consider the diagnosis of TRAP the indication for fetal intervention (Tsao et al. 2002).
Various percutaneous procedures have been described to interrupt the umbilical circulation in acardiac twins, including (1)insertion of a thrombogenic coil into the recipient twin’s umbilical cord, (2) injection of silk soaked in alcohol into the cord, (3) injection of absolute alcohol into the cord, (4) fetoscopic ligation of the acardiac fetus’s cord, (6) bipolar forceps cautery of the acardiac fetus’s cord, (7) thermocoagulation of the aorta of the acradiac fetus, and (8) intrafetal radiofrequency thermablation (Porreco et al. 1991; Holzgreve et al. 1994; Quintero et al. 1994; Sepulveda et al. 1995; Arias et al. 1998; Rodeck et al. 1998; Challis et al. 1999; Tsao et al. 2002; Livingston et al. 2007).
Injection of coils or slerosants is generally no longer performed because of the unreliability in achieveing complete occlusion. Fetoscopic cord ligation may be associated with a failure rate of 10% together with a 30% risk of preterm rupture of membranes (Challis et al. 1999). Laser and cautery options have the advantage of generally requiring one access port in the uterus and therefore may be associated with less morbidity.
Robie et al. (1989) reported a case of selective delivery by hysterotomy of an acardiac acephalic twin fetus at 22.5 weeks of gestation with the subsequent delivery of the normal twin at 33 weeks of gestation. Fries et al. (1992) subsequently reported 5 cases of selective delivery in 1992. In one case, placental abruption occurred shortly after the procedure, leading to fetal death. Two cases delivered at 35 weeks of gestation, and the remaining 2 delivered at 27 and 28 weeks.
Porreco et al. (1991) described the insertion of a helical metal coil under sonographic guidance to induce thrombosis in the umbilical artery of the acardiac twin at 24 weeks. The co-twin delivered at 39 weeks and had a normal course.
Quintero et al. (1994) described a percutaneous fetoscopic procedure that treated this condition at 19 weeks of gestation and was followed by the birth of a normal twin at 36 weeks of gestation. A further case was reported by McCurdy et al. (1993). A trial of maternal digoxin administration failed and was followed by a fetoscopic ligation of the acardiac twin’s cord at 19 weeks. Ultrasound examination on the first postoperative day indicated death of the pump twin.
Holzgreve et al. (1994) injected multiple pieces of silk suture soaked in 96% alcohol into the umbilical cord of an acardiac twin at 21 weeks of gestation. This resulted in immediate interruption of flow in the cord and the ultimate delivery at term of a 2780-g healthy newborn. The advantage of this approach in comparison to umbilical-cord ligation is the use of a much thinner needle. Less operative time is required, and there is no need for general anesthesia (Holzgreve et al. 1994).
Other methods of interrupting the circulation in the acardiac twin involve direct coagulation of the umbilical vessels or the aorta, using either laser photocoagulation or diathermy themocoaglulation. Laser photocoagulation of umbilical vessels using a neodymium yttrium aluminum garnet laser has been successfully reported, although this approach appears less likely to be successful when performed after 24 weeks gestation (Arias et al. 1998). This may be because umbilical vessels are too large to adequately photocoagulate when the gestational age is greater than 24 weeks. Thermocoagulation of the aorta of the acardiac fetus using diathermy via a wire passed through an 18-gauge needle has been successfully reported in four cases at 24 weeks gestation or less (Rodeck et al. 1998). The advantages of this latter approach include avoiding the need for micro-endoscopic instruments or skills, and avoiding the difficulties in identifying the target umbilical cord. Intrafetal radiofrequency ablation (RFA) has also been utilized in cases of TRAP. RFA causes thermal injury with high frequency radiowaves that denature proteins and initiate cell death through coagulative necrosis. In a series of 23 pregnancies complicated by TRAP and managed with RFA, there was a 91% survival rate with a mean gestational age of 35 weeks at delivery (Lee et al 2004). Livingston and Crombleholme et al. reported a 95% survival rate with an ultrasound-guided technique using a 17-gauge radiofrequency LeVeen needle (Boston Scientific) with a mean gestational age at delivery of 36 weeks in a series of 26 patients. Survival rates of 85% have been reported with fetoscopic cord coagulation likely as a consequence of two ports being required (Lewi et al. 2003). More recently, Dr Crombleholme’s experience with radiofrequency ablation for TRAP sequence in 54 fetuses in which the acardius to pump twin ratio exceeded 0.7, there was evidence of increased combined ventricular output, or polyhydramnios in the pump twin was successful with 97.3% pump twin survival and delivery at a mean gestational age of 36.5 weeks. It is important to note that the success rate for radiofrequency ablation for other indications such as anomalous co-twin is significantly lower at 85%. We suspect that this is due to the high rate of blood flow in the vessels of anomalous co-twins compared to an acardius. The higher blood flow dissipates the heat generated by the RFA needs and makes it harder to coagulate. Conversely, in TRAP sequence the reversed blood flow in the typically single umbilical artery cord of the acardius is usually sluggish and less able to dissipate the heat generated by the RFA needles and coagulation is more efficient.
The timing of fetal intervention in TRAP sequence remains controversial. Older data suggests that the acardius to pump twin ration greater than 70% predicts a 90% pregnancy complication rate combining fetal loss and/or serve premature delivery. Lewi et al, have reported that there is a 33% rate of fetal demise of the pump twin by 18 weeks in TRAP managed expectantly (Lewi et al 2010). This raised the question of treating TRAP sequence prophylactically without waiting for the pregnancy to meet criteria for intervention. Our own experience with TRAP has shown that with appropriate surveillance in the absence of acardius:pump twin ratio >70%, that fetal loss, polyhydramnios and preterm delivery are extremely rare events. Aiken et al, however, has proposed prophylactic treatment of acardius at the time of diagnosis even when less than 16 weeks’ gestation. There have been now at least 3 case reports of TRAP sequence being treated prophylactically at <16 weeks (Aikin et al 2014, Cabassa et al 2014, Paramasivam et al 2010). Usually this has been by intrafetal radiofrequency ablation , but interstitial laser photocoagulation has also been reported in among these early gestation cases (Pagani et al 2014). In a series of 17 cases treated between 15 and 18 weeks gestation with interstitial laser Pagani reported an 82% pumpt twin survival with two cases having to be re-treated due to recanalization and persistent blood flow to the acardius. In this series cases managed expectantly, had an intrauterine fetal demise before 15 weeks’ gestation suggesting the early diagnosis of TRAP may identify a subset of TRAP pregnancies at greater risk (Pagani et al 2014).
The approach at the Fetal Care Center of Dallas is to offer radiofrequency ablation in cases of TRAP sequence in which the acardius to pump twin ratio exceeds 70%, there is polyhydramnios, or elevated combined ventricular output (>600 ml/kg/min). Using these criteria we have had a 97.5% pump twin survival rate with radiofrequency ablation. In addition, using these criteria, we have not had a pump twin loss during expectant management who did not meet these criteria. It is important to note that the majority of our patients present at 18 week or greater and it may well be that the natural history of TRAP presenting < 16 weeks could be different. There insufficient data to make recommendations about fetal intervention this early without meeting criteria, but prophylactic intervention may be justified in cases of early gestation presentation.
It has been suggested that successful interruption of the acardiac circulation after 24 weeks gestation may require a more invasive approach, such as fetoscopic ligation of the umbilical cord (Arias et al. 1998; NcCurdy et al. 1993; Quintero et al. 1994). However, the series reported both by Tsao and Livingston included patients successfully treated after 24 weeks’ gestation.
- Treatment of The Newborn
A neonatologist should attend the delivery. In Moore et al.’s (1990) series, admission to a newborn intensive care unit was required in 41% of the pregnancies and 59% of those reaching viability. Five of 29 live-born pump twins died during the newborn period. There is little information in the literature on the neonatal course of the pump twin. The main problems for the pump twin include complications of prematurity and congestive heart failure (Moore et al. 1990; Van Allen et al. 1983).
Other frequent neonatal findings include massive hepatosplenomegaly, ascites with hypoplasia of abdominal musculature, edema, and hypoalbuminemia due to inadequate liver synthesis of albumin (Van Allen et al. 1983).
Respiratory assistance as well as support of myocardial function with inotropic medication may be required. Early administration of surfactant therapy is indicated when premature delivery at less than 30 weeks of gestation is anticipated. Postnatal consultation with a pediatric cardiologist and echocardiography are recommended.
- Long-Term Outcome
There is no information in the literature concerning long-term outcome for the pump twin. Considerations for the long-term prognosis must include the degree of prematurity, the severity of the neonatal course, and the degree of congestive heart failure.
- Genetics and Recurrence Riskyoast
Estimates of the recurrence risk of acardiac twin pregnancy are on the order of 1 in 10,000 (Van Allen et al. 1983). This recurrence risk is calculated from the recurrence risk for monoamniotic twinning, which is 1% (Myrianthopoulos 1970), multiplied by the frequency of the occurrence of the TRAP sequence, which is approximately 1% of all monozygous twins (Gillim and Hendricks 1953; Napolitani and Schreiber 1960).
Ahlfeld F. Die Entstehung der Acardiaci. Arch Gynakol 1879;14:321.
Aitken, K, Andrews J, VanMieghem T, Windrim R, Kachura J, Ryan G: Early radiofrequency ablation for twin reversed arterial perfusion sequence: Case report and literature review. Gynecol Obstet 2014, 4:9-1-5
Allan LD. Manual of fetal echocardiography. Boston: MTP 1986.
Arias F, Sunderji S, Gimpleson R, et al. Treatment of acardiac twinning. Obstet Gynecol 1998;91:818–821.
Ash K, Harman CR, Gritter H. TRAP sequence—successful outcome with indomethacin treatment. Obstet Gynecol 1990;76:960.
Bieber FP, Nance WE, Morton CC, et al. Genetic studies of an acardiac monster: evidence of polar body twinning in man. Science 1981;213:755.
Benirschke K, Kim CK. Multiple pregnancy. Part I. N Engl J Med 1973;288:1276–1284.
Benson CB, Bieber FR, Genest DR, et al. Doppler demonstration of reversed umbilical blood flow in an acardiac twin. J Clin Ultrasound 1989;17:291–295.
Berg C, Hoist D, Mallmann MR, Gottschalk I, Gembruch U et al: Early vs late intervention in win reversed arterial perfusion sequence. Ultrasound Obstet Gynecol 2014, 43 :60-64
Billah KL, Shah K, Odwin C. Ultrasonic diagnosis and management of acardius acephalus twin pregnancy. Med Ultrasound 1984;8:108.
Brassard M, Fouron JC, Leduc l, et al. Prognostic markers in twin pregnancies with an acardiacfetus. Obstet Gynecol 1999; 94: 409-414.
Cardwell MS. The acardiac twin, a case report. J Reprod Med 1988;33:320–322.
Cabassa P, Fishera VA, Prefumo F, Taddei F, Gandolfi S et al: The use of radiofrequency ablation for twin-reversed arterial perfusion sequence: A case series and review of the literature. Eur J Obstet Gynecol Reprod Biol 2013, 166: 127-132
Challis D, Gratacos E, Deprest JA: Cord occlusion techniques for selective termination in monochorionic twins. J Perinat Med 27(5):327-338, 1999.
D’Alton ME, Simpson LL. Syndromes in twins. In: Chervenak FA, D’Alton ME, eds. Multiple gestation. Semin Perinatol 1995;19:375–386.
Das K. Acardius anceps. Br J Obstet Gynaecol 1902;2:341.
Dashe JS, Fernandez CO, Twickler DM. Utility of Doppler velocimetry in predicting outcome in twin reversed-arterial perfusion sequence. Am J Obstet Gynecol 2001; 185: 135-139.
DeVore GR. Cardiac imaging. In: Sabbagha RE, ed. Diagnostic ultrasound. 2nd ed. Philadelphia: Lippincott 1987: 324–362.
Donnenfeld AE, van de Woestijne J, Craparo F, et al. The normal fetus of an acardiac twin pregnancy: perinatal management based on echocardiographic and sonographic evaluation. Prenat Diagn 1991;11: 235–244.
Fisk NM, Ware M, Stanier P, et al. Molecular genetic etiology of twin reversed arterial perfusion sequence. Am J Obstet Gynecol 1996;174:891–894.
Fries MH, Goldberg JD, Golbus MS. Treatment of acardiac-acephalus twin gestations by hysterotomy and selective delivery. Obstet Gynecol 1992;79:601–604.
Gillim DL, Hendricks CH. Holocardius: review of the literature and case report. Obstet Gynecol 1953;2:647.
Haring DAJP, Cornel MC, Van der Linden JC, et al. Acardius acephalus after induced ovulation: a case report. Teratology 1993;47:257–262.
Healey MG. Acardia: predictive risk factors for the co-twin’s survival. Teratology 1994;50:205–213.
Holzgreve W, Tercanli S, Krings W, et al. A simpler technique for umbilical-cord blockade of an acardiac twin. N Engl J Med 1994;331:56–57.
James WH. A note on the epidemiology of acardiac monsters. Teratology 1977;16:211–216.
Kappelman MD. Acardius amorphus. Am J Obstet Gynecol 1944;47:412.
Kinsel-Ziter ML, Cnota JF, Crombleholme TM, et al. Twin reversed arterial perfusion sequence: pre- and post-operative cardiovascular findings in the pump twin. Ultrasound in Obstet Gynecol 2009, in press.
Lachman R, McNabb M, Furmanski M, et al. The acardiac monster. Eur J Pediatr 1980;134:195.
Langlotz H, Sauerbrei E, Murray S. Transvaginal Doppler sonographic diagnosis of an acardiac twin at 12 weeks gestation. J Ultrasound Med 1991;10:175–179.
Lewi L, Valencia C, Gonzalez E, Deprest J, Nicolaides KH: the outcome of twin reversed arterial perfusion sequence diagnosed in the first trimester. Am J Obstet Gynecol 2010: 203: 213-218
Lee H, Wagner A, Ball R, et al. Radiofrequency ablation for TRAP sequence. Am J Obstet Gynecol2004; 191: S18.
Lee H, Bebbington M, Crombleholme TM: The North American Fetal Therapy Network Registry Data on outcomes of radiofrequency ablation for twin-reversed arterial perfusion sequence. Fetal Diagn Ther 2013, 33: 224-229
Lewi L, Gratacos E, Ortibus E, et al. Pregnancy and infant outcome of 80 consecutive cord coagulation in complicated monochorionic multiple pregnancies. Am J Obstet Gynecol 2006;194:782-789.
Livingston JC, Lim FY, Polzin W, et al. Intrafetal radiofrequency ablation for twin reversed arterial perfusion (TRAP): a single-center experience. Am J Obstet Gynecol 2007;197:399.e1-3.
Mack LA, Gravett MG, Rumack CM, et al. Antenatal ultrasonic evaluation of acardiac monsters. J Ultrasound Med 1982;1:13–18.
Malone FD, D’Alton ME. Anomalies peculiar to multiple gestations. Clin Perinatol 2000; 27: 1033-1046.
McCurdy CM Jr, Childers JM, Seeds JW. Ligation of the umbilical cord of an acardiac-acephalus twin with an endoscopic intrauterine technique. Obstet Gynecol 1993; 82:708–711.
Moore TR, Gale S, Benirschke K. Perinatal outcome of forty-nine pregnancies complicated by acardiac twinning. Am J Obstet Gynecol 1990;163:907–912.
Myrianthopoulos NC. An epidemiologic survey of twins in a large, prospectively studied population. Am J Hum Genet 1970;22:662.
Napolitani FD, Schreiber I. The acardiac monster: a review of the world literature and presentation of 2 cases. Am J Obstet Gynecol 1960;80:582.
Pagani G, D’Antonio F, Khalil A, Papegeorghiou A, Bhide A et al: Intrafetal laser for twin reversed arterial perfusion sequence: cohort study and meta-analysis. Ultrasound Obstet Gynecol 2013, 42: 6-14
Platt LD, DeVore GR, Bieniarz A, et al. Antenatal diagnosis of acephalus acardia: a proposed management scheme. Am J Obstet Gynecol 1983;146:857.
Porreco RP, Barton SM, Haverkamp AD. Occlusion of umbilical artery in acardiac, acephalic twin. Lancet 1991; 337:326–328.
Pretorius DH, Leopold GR, Moore TR, et al. Acardiac twin: report of Doppler sonography. J Ultrasound Med 1988; 7:413.
Quintero RA, Rich H, Puder K, et al. Umbilical-cord ligation of an acardiac twin by fetoscopy at 19 weeks gestation. N Engl J Med 1994;330:469–471.
Robie GJ, Payne GG, Morgan MA. Selective delivery of an acardiac, acephalic twin. N Engl J Med 1989;320:512.
Rodeck C, Deans A, Jauniaux E. Thermocoagulation for the early treatment of pregnancy with an acardiac twin. N Engl J Med 1998;339:1293–1295.
Schatz CF. Die Acardii und ihre Verwandten. Berlin: A. Hirschwald, 1898.
Shenker L, Reed KL, Marx GR, et al. Fetal cardiac Doppler flow studies in prenatal diagnosis of heart disease. Am J Obstet Gynecol 1988;158:1267–1273.
Sherer DM, Armstrong B, Shah YG, et al. Prenatal sonographic diagnosis, Doppler velocimetric umbilical cord study, and subsequent management of an acardiac twin pregnancy. Obstet Gynecol 1989;74:472–475.
Silverman NH, Kleinman CS, Rudolph AM, et al. Fetal atrioventricular valve insufficiency associated with nonimmune hydrops: a two dimensional echocardiographic and pulse Doppler ultrasound study. Circulation 1985;72:825–831.
Simonds JP, Gowen GA. Fetus amorphus: report of a case. Surg Gynecol Obstet 1925;41:171.
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 1983;147:842–844.
Sogaard K, Skibsted L, Brocks V. Acardiac Twins: pathophysiology, diagnosis, outcome, and treatment. Fetal Diagn Ther 1999; 14: 53-59.
Sullivan AE, Varner MW, Ball RH, Jackson M, Silver RM. The management of acardiac twins: a conservative approach. Am J Obstet Gynecol 2003; 189: 1310-1313.
Tsao KJ, Feldstein V, Albanese CT et al: Selective reduction of acardiac twin by radiofrequency ablation. Am J Obstet Gynecol 187(3):635-640, 2002
Van Allen MI, Smith SW, Shepard TH. Twin reversed arterial perfusion (TRAP) sequence: a study of 14 twin pregnancies with acardius. Semin Perinatol 1983;7:285.
Figure 1. Gradation of loss of normal body form in acardia. (Reprinted, with permission, from Van Allen MI, Smith SW, Shepard TH. Twin reversed arterial perfusion (TRAP) sequence: a study of 14 twin pregnancies with acardius. Semin Perinatol 1983;7:288.) (PICK UP FIG 118-1 FROM PAGE 886) Pick up and redraw fig 118-1, p886.
Figure 2. An acardiac fetus and its pump twin delivered at 26 weeks of gestation following spontaneous premature labor. (PICK UP FIG 118-2 FROM PAGE 887 1ST EDITION, BUT NOTE THAT DR D’ALTON HAS COLOR VERSION OF THIS TO BE USED INSTEAD) pick up 118-2, p887. Mary and Karin, please check for color version.
Figure 3. Prenatal ultrasound image of TRAP pregnancy at 22 weeks with amorphous mass (arrow) connected through placental surface vessel from umbilical cord of pump fetus.