Acardia: predictive risk factors for the co-twin's survival

Fetal magnetic resonance imaging, ultrasound, and echocardiography findings in twin reversed arterial perfusion sequence

BACKGROUND

Twin reversed arterial perfusion (TRAP) sequence is a rare complication of monochorionic multiple gestation pregnancies, in which the pump twin provides hemodynamic support to a nonviable co-twin (acardius). Fetal magnetic resonance imaging (MRI) is used to detect pump twin abnormalities, particularly brain ischemia, prior to fetal intervention to interrupt umbilical blood flow to the acardius.

OBJECTIVE

To summarize the imaging findings of TRAP sequence pregnancies in a large series.

MATERIALS AND METHODS

A single-center retrospective review was performed of all TRAP sequence pregnancies referred for fetal MRI (2004-2021). Fetal MRI, ultrasound, and echocardiography data were collected.

RESULTS

Eighty-eight TRAP sequence pregnancies with MRI were included (mean gestational age, 19.8±2.8 weeks). Demise of the pump twin was noted in two pregnancies at the time of MRI. By MRI, 12% (10/86) of live pump twins had abnormalities, including 3% (3/86) with brain abnormalities and 9% (8/86) with extra-cranial abnormalities. By echocardiography, 7% (6/86) of pump twins had structural cardiac abnormalities. Three acardius morphological subtypes were identified by MRI: acephalus (55%, 48/88), anceps (39%, 34/88), and amorphous (7%, 6/88). The mean ultrasound acardius to pump twin ratio A/P ratio, calculated for each twin pair as the ratio of the acardius trunk (and head, if present) plus limb volume to the pump twin estimated fetal weight) differed among the three acardius subtypes (P=.03). The mean A/P ratio moderately correlated with pump twin cardiothoracic ratio and combined cardiac output (Pearson's r=0.45 and 0.48, respectively, both P<.001).

CONCLUSION

Fetal MRI of TRAP sequence pregnancies found anomalies in a substantial number of pump twins. The three acardius subtypes differed in A/P ratio, which moderately correlated with the pump twin cardiothoracic ratio and combined cardiac output.

Novel autopsy and genetic findings in an acardiac twin: case report and literature review

Twin reversed arterial perfusion (TRAP) sequence is a rare complication of monochorionic twinning whereby a donor twin perfuses an acardiac twin via aberrant vascular anastomoses. The resulting paradoxical retrograde blood flow supplying the acardiac twin is oxygen-poor, leading to some of the most severe malformations encountered in humans. Though the first descriptions of acardiac twins date back to at least the 16th century, the pathophysiologic processes which underpin the development of TRAP sequence are still being elucidated. Theories on the pathogenesis of TRAP sequence include deficiencies intrinsic to the embryo and primary abnormalities of the placental vasculature. Autopsy studies continue to provide clues to the underlying pathogenesis of TRAP sequence, and the characterization of the spectrum of manifestations that can be observed in acardiac twins. Herein, we present the clinical, autopsy, and molecular findings in a unique case of TRAP sequence. Novel findings include a primitive cloaca-like structure and chromosomal aberrations involving 6q11.1 and 15q25.1.

Use of holmium laser for umbilical cord transection in a monoamniotic pregnancy threatened by an acardiac co-twin: a case report

Background

Twin reversed arterial perfusion sequence is a rare complication of monochorionic multifetal pregnancies. In this syndrome, the acardiac twin has a nonfunctional heart, while the other twin, the pump twin, has normal development. The pump twin perfuses the acardiac twin and is therefore at risk for cardiac decompensation. In monoamniotic cases, the normal co-twin is also at risk of sudden death due to cord entanglement. Treatment consists of coagulation and transection of the acardiac’s umbilical cord. We report the first intrauterine use in pregnancy of a Ho:yttrium aluminum garnet laser to safely and successfully transect the umbilical cord after Nd:yttrium aluminum garnet coagulation.

Case presentation

A 30-year-old Caucasian woman was referred to our fetal–maternal medicine unit at 9 weeks gestation with a monochorionic–monoamniotic twin pregnancy complicated by an acardiac twin. After counseling, she opted for an elective intervention to minimize the risks to the pump twin. At 16 weeks, fetoscopy was performed using a single 2-mm entry port. Through this port, a 1.0-mm fetoscope and a 0.365-mm laser fiber were introduced. Under fetoscopic sight and ultrasound (Doppler) guidance, the umbilical cord of the acardiac twin was first coagulated by laser energy using a Nd:yttrium aluminum garnet laser and then, using the same fiber, transected using a Ho:yttrium aluminum garnet laser. The patient underwent cesarean section at 38 weeks and delivered a healthy baby.

Conclusions

We present the first report on intrauterine use of an Ho:yttrium aluminum garnet laser in human pregnancy. Ho:yttrium aluminum garnet laser energy can be successfully and safely used for umbilical cord transection and carries fewer risks than other methods of transection.

Hypothesized pathogenesis of acardius acephalus, acormus, amorphus, anceps, acardiac edema, single umbilical artery, and pump twin risk prediction

Background

Acardiac twinning complicates monochorionic twin pregnancies in ≈2.6%, in which arterioarterial (AA) and venovenous placental anastomoses cause a reverse circulation between prepump and preacardiac embryos and cessation of cardiac function in the preacardiac. Literature suggested four acardiac body morphologies in which select (groups of) organs fail to develop, deteriorate, or become abnormal: acephalus (≈64%, [almost] no head, part of body, legs), amorphus (≈22%, amorphous tissue lump), anceps (≈10%, cranial bones, well‐developed), and acormus (≈4%, head only). We sought to develop hypotheses that could explain acardiac pathogenesis, its progression, and develop methods for clinical testing.

Methods

We used qualitatively described pathophysiology during development, including twin‐specific AA and Hyrtl's anastomoses, the short umbilical cord syndrome, high capillary permeability, properties of spontaneous aborted embryos, and Pump/Acardiac umbilical venous diameter (UVD) ratios.

Results

We propose that each body morphology has a specific pathophysiologic pathway. An acephalus acardius may be larger than an anceps, verifiable from UVD ratio measurements. A single umbilical artery develops when one artery, unconnected to the AA, vanishes due to flow reduction by Hyrtl's anastomotic resistance. Acardiac edema may result from acardiac body hypoxemia combined with physiological high fetal capillary permeability, high interstitial compliance and low albumin synthesis. Morphological changes may occur after acardiac onset. Pump twin risk follows from UVD ratios.

Conclusion

Our suggested outcomes agree reasonably well with reported onset, incidence, and progression of acardiac morphologies. Guidance for clinical prediction and testing requires ultrasound anatomy/circulation study, from the first trimester onward.

Monochorionic monoamniotic twin pregnancies

Monoamniotic twin pregnancies are rare, but early diagnosis of such pregnancies is critical, as the incidence of complications in these pregnancies is much higher than in diamniotic or dichorionic twin pregnancies. Overall, only 70% of all monoamniotic twins will survive. Furthermore, approximately half of fetal deaths in these pregnancies are because of the high incidence of fetal anomalies (15%-25%), such as twin reversed arterial perfusion sequence and conjoined twinning. Therefore, early anatomy screening in the first trimester of pregnancy is recommended. Other causes of fetal death in these pregnancies include twin-twin transfusion syndrome, tight cord entanglement, or acute hemodynamic imbalances through the large placental vascular anastomoses. After viability, fetal surveillance can be intensified, as this decreases the risk of in utero death. Both inpatient and outpatient surveillance are reasonable. If otherwise uncomplicated, monoamniotic twins should be delivered at 33 to 34 weeks' gestation. Most centers will deliver by cesarean delivery, but some continue to advocate for vaginal delivery. Lastly, neonatal morbidity is high in monoamniotic twin pregnancies and is mainly related to prematurity.

A Taiwan's experience: A case report and review of literature of successful early intrauterine treatment with radiofrequency ablation in twin reversed arterial perfusion (TRAP) sequence

Acardiac twin or twin reversed arterial perfusion (TRAP) sequence is a rare medical complication of Monozygotic twins. Taiwanese Obstetricians usually treat TRAP sequence conservatively. Occasionally, repeated amnio-reduction is performed to decompress the polyhydramnios caused by the TRAP sequence, even though there was no correction of the pathophysiologic mechanism. Radiofrequency ablation is a minimally invasive, percutaneous technique that can effectively obliterate blood supply to an acardiac twin to preserve and protect the pump twin. This recent technique has never been used before for the treatment of the TRAP sequence in Taiwan. This article reported the first-hand experience of acardiac twin management with RFA in Taipei Chang Gung Memorial Hospital.

Why does second trimester demise of a monochorionic twin not result in acardiac twinning?

Background

We previously explained why acardiac twinning occurs in the first trimester. We raised the question why a sudden demised monochorionic twin beyond the first trimester does not lead to acardiac twinning. We argued that exsanguinated blood from the live twin would strongly increase the demised twins' vascular resistance, preventing its perfusion and acardiac onset. However, our current hypothesis is that perfusion of the demised twin does occur but that it is insufficient for onset of acardiac twinning.

Methods

We analyzed blood pressures and flows in a vascular resistance model of a monochorionic twin pregnancy where one of the fetuses demised. The resistance model consists of a demised twin with a (former) placenta, a live twin and its placenta, and arterioarterial (AA) and venovenous placental anastomoses. We assumed that only twins with a weight of at least 33% of normal survived the first trimester and that exsanguination of more than 50% of its blood volume is fatal for the live twin.

Results

At 20 weeks, only AA anastomoses with radii ≲1 mm keep the exsanguinated blood volume below 50%. Then, perfusion of the deceased body with arterial blood from the live fetus is about 5–40 times smaller than when that body was alive. Beyond 20 weeks, this factor is even smaller. At 14 weeks, this factor is at most 2.

Conclusion

We hypothesize that this small perfusion flow of arterial blood prevents further growth of the deceased body and hence precludes onset of acardiac twinning.

Monochorionic Triplet Pregnancies With Twin Reversed Arterial Perfusion and Acardiac Triplet: Report of Two Cases and Literature Review

TRAP pregnancies involving monochorionic triplets are extremely rare, calculated to be 1 in 4.5 million. We report two cases of monochorionic triplet pregnancies with an acardiac triplet. In one case, the mother was a 33-year-old G2P1 who underwent dilation and evacuation at 20 weeks due to poor prognosis. The other case involved a 21-year-old G1P0 mother presenting in advanced preterm labor at 21 weeks who elected expectant management. Seventeen cases of monochorionic triplets with TRAP were identified in the literature. Invasive intervention was performed in 10 cases; 9 cases resulted in the survival of the nonacardiac twins and 1 case resulted in the survival of 1 fetus. Our two cases had common sonographic features which included polyhydramnios of all fetuses. Placental features shared between both cases included being large for gestational age and velamentous insertion of the acardiac twin. The acardiac twins in both of our cases were hydropic and demonstrated developed pelvis and lower extremities. One had an omphalocele. Most case reports in the literature review demonstrate similar findings. Two cases of monochorionic triplets with TRAP and acardiac twin are herein described. Successful treatment by invasive interventions have been described in this condition, highlighting the importance of early diagnosis.

Acardiac twin pregnancies part VI: Why does acardiac twinning occur only in the first trimester?

BACKGROUND

Clinical observation suggests that acardiac twinning occurs only in the first trimester. In part, this contradicts our previous analysis (part IV) of Benirschke's concept that unequal embryonic splitting causes unequal embryo/fetal blood volumes and pressures. Our aim is to explain why acardiac onset is restricted to the first trimester.

METHODS

We applied the vascular resistance scheme of two fetuses connected by arterio-arterial (AA) and veno-venous (VV) anastomoses, the small VV resistance approximated as zero. The smaller twin has volume fraction α < 1 of the assumed normal larger twin, and has only access to fraction X < 1 of its placenta; the larger twin's larger mean arterial pressure accesses the remaining fraction. Before 13 weeks, embryos have a much smaller vascular resistance than placentas. After 13 weeks, when maternal blood provides oxygen, smaller twins can increase their vascular volume by hypoxemia-mediated neovascularization. Estimated AA radii at 40 weeks, r_AA (40), are 0.5-1.3 mm.

RESULTS

Embryos with α < 0.33 unlikely survive 13 weeks and acardiac twinning occurs under appropriate conditions (AA-VV, small placenta). Acardiac body perfusion occurs because of a much smaller vascular resistance than the placenta. When α > 0.33 and r_AA (40)=1.3 mm, modeled survival is >32 weeks.

CONCLUSION

Before 13 weeks, embryos with α < 0.33 cannot survive and may result in the onset of acardia. Beyond 13 weeks, fetuses with α ≥ 0.33 survive because r_AA (40) is too small for acardiac onset. Following fetal demise, exsanguination from the live twin increases its blood volume and, we assumed also, its vascular resistance. Perfusion then occurs through the lower resistance placenta.

Acardiac twin pregnancies part V: Why does an acardiac twin with renal tissue produce polyhydramnios?

Background

Acardiac twinning is a complication of monochorionic twin pregnancies. From literature reports, 30 of 41 relatively large acardiac twins with renal tissue produced polyhydramnios within their amniotic compartment. We aim to investigate the underlying mechanisms that cause excess amniotic fluid using an established model of fetal fluid dynamics.

Methods

We assumed that acardiac onset is before 13 weeks, acardiacs with renal tissue have normal kidney function and produce urine flow from 11 weeks on, and acardiac urine production requires a pressure of half the pump twin's mean arterial pressure. We apply a resistance network with the pump twin's arterio‐venous pressure as source, pump umbilical arteries, placenta, placental arterio‐arterial (AA) anastomoses and acardiac resistances. Acardiac amniotic fluid dynamics excluded acardiac lung fluid secretion, swallowing and the relatively small intramembranous flow.

Results

In small acardiacs with sufficient urine production, polyhydramnios will occur due to the lack of amniotic fluid resorption. Urine production is dependent upon having sufficient mean arterial pressure, which requires nearly a two‐fold larger resistance within the acardiac as compared to the placental AA resistance. Subphysiologic arterial pressure may result in renal dysgenesis.

Conclusion

Our findings suggest the potential for prediction of which clinical acardiac cases may or may not develop polyhydramnios based upon noninvasive assessments of renal tissue, blood flow and urine production. This information would be of great value in determining early obstetric interventions as opposed to conservative management. These findings may also contribute to an improved knowledge of the fascinating pathophysiology that surrounds acardiac twinning.

Placental Anatomy and Function in Twin Gestations

With an increasing incidence of twin gestations, understanding the inherent risks associated with these pregnancies is essential in modern obstetrics. The unique differences in placentation in twins contribute to the increased risks. Monochorionic twins are susceptible to complications because of their unique placental architecture, including twin-to-twin transfusion syndrome, the twin anemia-polycythemia sequence, selective intrauterine growth restriction, and the twin reversed arterial perfusion sequence. Knowing the clinical correlations of placental anatomy in these gestations helps perinatal pathologists perform a more informed placental evaluation, allowing for better care for the mother and her children.

Acardius anceps with neck cyst and cleft palate: Three dimensional skeletal computed tomography reconstruction with discussion of the literature

Acardiac twinning is a rare anomaly of monochorionic twin pregnancies. Acardiac fetuses lack a functional heart but are passively perfused by arterial blood from their pump co-twin causing the acardiac body to be hypoxemic. In this report, we present an acardius anceps, therapeutically laser separated from its pump twin at 16 weeks. The healthy pump twin and macerated acardiac body were born at 40 3/7 weeks. A three dimensional (3D) reconstruction was made by CT images, showing cranial bones, spinal column, pelvis and lower extremities but absent arms. A cyst in the neck of the acardiac twin was identified by postnatal sonography; this was also described in four literature cases, and was additionally observed by us in two other acardiac twins. Median cleft palate was identified by oral cavity inspection but undetectable in the reconstruction. In the literature, we found 21 other acardiac anceps twins with a cleft palate. From the two larger published series, with 12 clefts in 21 acardiac anceps twins, a cleft palate occurs in over 50% during acardiac twinning. Our first hypothesis is that acardiac fetuses develop an oral cleft palate when acardiac onset starts prior to 11 weeks, because 11 weeks includes the period of embryonic oral cavity formation, and no cleft occurs when onset starts later than 11 weeks. Our second hypothesis is that cysts and cleft palates are more common in acardiac twins than currently known, likely reflecting that acardiac bodies are hypoxemic and that hypoxia contributes to the development of both cysts and clefts.

Spontaneous triplet pregnancy and trap sequence, case report

BACKGROUND

Spontaneous multiple pregnancies are rare, and the incidence of spontaneous triplet pregnancy is about 1/4000. TRAP (Twin Reversed Arterial Perfusion) sequence has acardiac foetus with non-viable multiple anomalies, and there is a pump foetus which feeds this foetus with placental anastomoses. TRAP sequence phenomena is quite rare in triplet pregnancies.

CASE PRESENTATION

The patient who applied to our clinic was 30 years old. Monochorionic diamniotic triplet pregnancy was detected by ultrasonographic examination. First amniotic sac had one foetus (Foetus A). Ultrasonographic evaluation of Foetus A revealed gestational age of 31 weeks, adequate amniotic fluid and no fetal structural anomalies. The second amniotic sac contained 2 foetuses and polyhydromnios. Ultrasonic measurements of Foetus B were consistent with 32 weeks gestational age. Color flow doppler indicated Foetus B was the pump foetus. Foetus C was an acardiac foetus with no sonographic visualization of cranium, thoracic organs or extremities, but abdominal circumference consistent with 28 weeks. Pregnancy was followed conservatively and evaluated regularly by ultrasonography twice a week. When prolonged bradycardia was detected in fetus B at 35 4/7 weeks, emergency cesarean section was performed. Two healthy fetuses weighing 2 kg were delivered each with an 8/10 APGAR score (Appearance, Pulse, Eye Insertion, Activity, Respiration).

CONCLUSION

This case was managed without any invasive procedures and demonstrates that treatment of TRAP sequence cases can be individualized considering clinical conditions, the size of the acardia twin and extent of placental venous anastomoses.

Acardiac twin pregnancies part IV: Acardiac onset from unequal embryonic splitting simulated by a fetoplacental resistance model

BACKGROUND

Benirschke postulated that acardiac twinning occurs when markedly unequal embryonic splitting combines with arterioarterial (AA) and venovenous placental anastomoses. We tested this hypothesis by model simulations and by comparison of outcomes with 18 "pseudo-" (twin fetus with beating heart but otherwise with clear signs of an acardiac) and 3 "normal" acardiac cases.

METHODS

The smaller/larger cell volume ratio at embryonic splitting becomes the smaller/larger embryonic/fetal blood volume ratio (a). From a, we derived nonpulsating blood pressures using normal values (larger twin) and normal values at an appropriate earlier gestational age (smaller twin). These unequal pressure sources were used in a linear resistance fetoplacental network to calculate umbilical venous diameter ratios. Acardiac onset occurs when the smaller twin has 50% left of its normal, singleton placenta. Comparison with clinical cases approximated a by crown-rump-length-ratio to the 3rd power. Input parameters are a and the AA-radius at 40 weeks.

RESULTS

Acardiacs can be small or large, can occur early or late, earlier at smaller a and larger AA, with larger umbilical venous diameter ratios at smaller a and smaller AA. Comparison with the 21 clinical cases was good, except for 2.

CONCLUSION

Our analysis supports Benirschke's hypothesis. The smaller twin has to share its placental perfusion with the larger twin, which is a novel finding. The AA size is essential for the future of both fetuses but complicates easy understanding of (pseudo-)acardiac clinical presentations. Late acardiac onset occurs infrequently. Using nonpulsating circulations may have caused our extensive predictions of late onset. An improved model requires including hypoxemia in the smaller twin from chronic placental hypoperfusion. Birth Defects Research 109:211-223, 2017. © 2016 Wiley Periodicals, Inc.

Role of ultrasonography in the management of twin gestation

Twins represent 1%-2% of all pregnancies, yet continue to account for a disproportionate share of neonatal adverse events including neonatal intensive care admission, morbidity, and mortality. Ultrasonography is central to the proper diagnosis of the type of twinning. Ideally, ultrasonography is performed before 14 weeks of gestation to determine chorionicity and amnionicity. Correct identification of the chorionicity in a twin pregnancy facilitates proper counseling and management of the gestation, including ultrasonography follow-up. Herein, the different types of twinning are reviewed, together with the implications for ultrasonography monitoring of each specific type of twin gestation.

Twin Reversed Arterial Perfusion: To Treat or Not?

Acardiac twinning or Twin Reverse Arterial Perfusion (TRAP)-sequence is a rare complication of monochorionic twin pregnancy. Whether to start elective or therapeutic treatment in TRAP-sequence is still controversial. In the present case, acardiac twin was not diagnosed till her delivery at 39 weeks. A healthy baby weighing 2.45 kg was delivered along with another amorphous mass (acardiac twin) of about 150 g which was attached to the placenta with a short and separate cord. As outcome of normal twin vary according to the growth of acardiac twin, frequent follow-up of the normal twin is required to look for the features of heart failure. Hence, the diagnosis of acardiac twin is essential in early pregnancy.

Forty cases of twin reversed arterial perfusion sequence treated with radio frequency ablation using the multistep coagulation method: a single-center experience

OBJECTIVE

To report the pregnancy outcomes of patients with twin reversed arterial perfusion (TRAP) sequence treated by radiofrequency ablation (RFA).

METHODS

This was a retrospective study of TRAP sequences treated in a single center between March 2002 and February 2015. Forty patients underwent RFA with expandable tines through a multistep coagulation method between 15 and 26 gestational weeks. The primary outcome was neonatal survival to discharge.

RESULTS

The overall survival of the pump twin was 85%. The survival rates in monochorionic-monoamniotic (MCMA) pregnancies and monochorionic-diamniotic pregnancies were 66.7% (4/6) and 87.9% (29/33), respectively. One triplet was treated successfully and delivered at 36 weeks of gestation. One of 35 live births (2.9%) had preterm premature rupture of membranes less than 34 weeks, resulting in infant death. In five intrauterine pump twin deaths, two cases were MCMA twins with cord entanglement, and three cases were MCDA twins with acardius anceps.

CONCLUSIONS

Our study supports the effectiveness of RFA for TRAP sequence after 15 weeks of gestation. The presence of MCMA twins or acardius anceps is associated with a high risk of pump twin death after RFA. © 2016 John Wiley & Sons, Ltd.

Conservative management in a case of uncomplicated trap sequence: a case report and brief literature review

INTRODUCTION

twin reversed arterial perfusion (TRAP) sequence is a rare anomaly that occurs in monochorionic twins with overall mortality rate ranging from 50% to 70% in the normal fetus, above all for congestive cardiac failure.

CASE REPORT

a 31-year-old Caucasian gravida was referred to our fetomaternal medicine unit in the 25 gestational age. Ultrasound examination revealed a monochorionic, biamniotic twin pregnancy with a donor fetus showing normal morphology and growth corresponding to gestational age. The recipient twin appeared grossly abnormal with no head, upper limbs, heart, or thoracic structures and massive, diffuse, soft tissue edema. Fetal Doppler and fetal echocardiography revealed normal parameters. The patient refused any treatment and was monitored with weekly ultrasonography and Doppler ultrasound examination. She underwent cesarean section due to premature labor/rupture of membranes secondary to a mild polyhydramnios, at 36 weeks gestational age and delivered an apparent normal female live baby weighing 2550 gr, and another female acardius acephalus twin, birth weight 1300 gr. This baby had rudimental edematous lower limbs, pelvic bone, lower sacral vertebrae, and absence of thorax and cephalic structures.

CONCLUSION

although the literature suggest that early intrafetal laser treatment of TRAP sequence is advantageous, our case shows that pregnancies referred late would still require a tailored approach after a risk-benefit assessment.

Intrafetal laser treatment for twin reversed arterial perfusion sequence: cohort study and meta-analysis

OBJECTIVES

To ascertain the outcome of twin reversed arterial perfusion (TRAP) sequence cases managed in our unit and to review systematically cases reported in the literature treated with intrafetal laser therapy.

METHODS

This was a retrospective cohort study of all TRAP sequence cases identified from 2000 to 2012 at our center. Pregnancy management and outcomes were ascertained from maternal and neonatal records. We also performed a meta-analysis of the literature on the use of intrafetal laser therapy for the treatment of TRAP. Adverse pregnancy outcome was defined as a composite of intrauterine death (IUD) and preterm birth before 37 weeks' gestation.

RESULTS

Twenty-three cases of TRAP were identified during the study period. Six were managed conservatively and 17 were treated with laser therapy. All cases managed conservatively were complicated by IUD at a median gestational age of 14 + 4 (interquartile range (IQR), 12 + 4 to 16 + 5) weeks. Among the treated cases, 14 (82%) delivered a healthy twin at a median gestational age of 37 + 1 (IQR, 34 + 0 to 38 + 3) weeks. Ten studies were reviewed in detail and the data were combined with those from the current study. The overall neonatal survival was 80%. Adverse pregnancy outcome was significantly lower when the treatment was performed before 16 weeks' gestation (19 vs 66%, P = 0.0025).

CONCLUSION

The study data demonstrate a high risk of spontaneous fetal demise in early pregnancy, lack of accurate prognostic markers and improved pregnancy outcome after laser therapy in cases of TRAP. In these cases we recommend elective treatment with intrafetal laser therapy at between 13 and 16 weeks' gestation.

Radiofrequency ablation as a minimally invasive procedure in the treatment of twin reversed arterial perfusion sequence in twin pregnancy

Twin reversed arterial perfusion sequence is a rare anomaly of monochorionic multiple pregnancies affecting 1 of 35,000 pregnancies and 1% of monochorionic twin pregnancies. In this condition the affected twin has lethal malformations including poor or absent heart development and is reversely perfused by a structurally normal co-twin. We report a case of a 21-year-old woman with a monochorionic twin pregnancy affected by twin reversed arterial perfusion sequence. This case highlights the therapeutic options and the management by radiofrequency ablation, which has been shown to be an easy and reliable technique with a high success rate compared with technically demanding fetoscopic procedures.

[Acardiac twins: pronostics markers' study]

OBJECTIVES

To determine ultrasonographic markers that can help to predict prognosis in twins acardiac pathology in order to manage it.

PATIENTS AND METHODS

A retrospective multicentric study has been led between 1997 and 2006. The following data were collected: frequency of monitoring, ultrasonographic markers studied according to the outcome of each pregnancy, associated with a review of the literature.

RESULTS

Six twin pregnancies with this condition were identified. The main studied criteria are: foetal growth of the pump twin, congestive heart failure, resistance index of the umbilical arteries, ductus venosus Doppler and middle cerebral artery peak velocity. There was no consensus concerning the method of ultrasonographic monitoring.

DISCUSSION AND CONCLUSION

According to our study and the literature, our management must take into account the ratio of (or the difference in) resistance indices between the twins, the middle cerebral artery peak velocity, the tricuspid regurgitation and the ratio of abdominal circumferences of the two twins.

[Multifoetal pregnancies complicated by reversed arterial perfusion: report of four cases]

INTRODUCTION

Twin reversed arterial perfusion syndrome (TRAP) or acardiac anomaly presents a rare and severe complication affecting monochorionic multiple pregnancies occurring in 1 per 35,000 pregnancies or 1 per 100 of monozygotic twins. We report four cases of multiple pregnancies with TRAP diagnosed over the last 2 years, which were under check-up and treatment during the entire pregnancy course finalized by delivery.

OUTLINE OF CASES

In two cases pregnancies were trigeminal, and other two geminal, with acardia of one foetus, by anceps type in three and acephalus in one. Expectant management was initially done in all cases. The relation of acardiac and donor abdominal circumference was below 50% and negative signs of the donor's cardiac failure were detected in two cases, so that expectative management was continued until delivery. Due to obstetric indications, a cesarean section was performed on the 33rd and 34th gestational week, and healthy newborns were delivered. Another two acardiac twins had abdominal circumference ratio between the acardiac fetus and the donor of over 50%, and signs of congestive heart failure in the donor, which indicated invasive therapeutic procedure with absolute alcohol chemisclerosis; it was done by alcohol injection into the acardiac abdominal aorta which interrupted the retrograde blood-flow into the acardiac umbilicus. In the first case a successful intervention was performed at 29th gestational week, but after 12 hours distress signs were registered. The delivery was finalized by a cesarean section, and a live donor was delivered. In the second case the intervention was successfully done at the 20th gestational week, and after 96 hours from the intervention lethal ending of the donor was registered.

CONCLUSION

Bearing in mind that the occurrence of TRAP is rare, it is necessary to sum-up experiences from a larger number of centres to determine efficient therapeutic procedure.

MRI findings in multifetal pregnancies complicated by twin reversed arterial perfusion sequence (TRAP)

BACKGROUND

Twin reversed arterial perfusion sequence (TRAP) is a rare complication in multifetal monochorionic pregnancies in which a normal "pump" twin provides circulation to an abnormal acardiac co-twin, resulting in high-output cardiac dysfunction in the pump twin.

OBJECTIVE

To define fetal MRI findings of TRAP sequence.

MATERIALS AND METHODS

Fetal MR images were retrospectively reviewed in 35 pregnancies complicated by TRAP sequence. Abnormalities of the pump twin, acardiac twin, umbilical cord, placenta and amniotic fluid were reviewed.

RESULTS

Acardiac twins were classified as: acephalus (51%), anceps (40%), amorphus (9%), acormus (0%). Common findings in acardiac twins include subcutaneous edema (77%), absent cardiac structures (86%), absent or abnormal thoracic cavity (100%), abnormal abdominal organs (100%), superior limbs absent (46%) or abnormal (51%), and inferior limbs present but abnormal (83%). There were pump twin findings of cardiac dysfunction in 43% and intracranial ischemic changes in 3%. Umbilical cord anomalies were present in 97%.

CONCLUSION

Acardiac twins present with a predictable pattern of malformation with poorly developed superior structures, more normally formed inferior structures and absent or rudimentary heart. Although usually absent, abnormal heart structures can be seen and do not exclude TRAP sequence. Pump twins are commonly normal with exception of findings of cardiac dysfunction and possible brain ischemia.

Twin reversed arterial perfusion (TRAP) sequence in association with VACTERL association: a case report

INTRODUCTION

Twin reversed arterial perfusion (TRAP) sequence is a rare complication of multiple pregnancy caused by defects in early embryogenesis. The pump twin supplies the acardiac recipient twin with blood, and although the pump twin is usually structurally normal, congenital anomalies have sometimes been reported. We report a unique case of twin reversed arterial perfusion sequence with a prenatal diagnosis of VACTERL association in the surviving pump twin.

CASE PRESENTATION

A 24-year-old Caucasian woman presented at 11 weeks' gestation with a monochorionic, monoamniotic twin pregnancy. A reversed arterial flow was noted on a Doppler imaging study coming from the larger, apparently normal twin to the smaller, grossly abnormal twin, and a diagnosis of twin reversed arterial perfusion sequence was made. Cardiac activity was undetectable in the recipient twin by 16 weeks' gestation. Further detailed assessment at 18 weeks' gestation revealed multiple congenital anomalies of the surviving pump twin, in keeping with a diagnosis of VACTERL association. A live infant girl was delivered at 39 weeks by elective cesarean section. She underwent extensive surgery with subsequent normal development at the age of two years.

CONCLUSION

The co-existence of two rare and complex conditions in this unique case raises interesting questions about the role of early defects in embryogenesis and their subsequent effects on fetal development. This case also highlights the importance of prenatal diagnosis of major congenital anomalies to the plan treatment, reduce morbidity and aid the survival of affected children.

Genetics and developmental pathology of twinning

Twin pregnancy is associated with a high risk of congenital malformations. This review covers the risk of such anomalies in both dizygotic and monozygotic twin pregnancies, and discusses current insights into the associations relating to zygosity, chorionicity and genetic factors. The pathological basis of specific malformations unique to the monochorionic twinning process, including conjoined twinning and twin reversed arterial perfusion (TRAP) sequence, is discussed in more detail, and factors contributing to the higher perinatal mortality rate in multiple pregnancies are addressed.

Specific complications of monochorionic twin pregnancies: twin-twin transfusion syndrome and twin reversed arterial perfusion sequence

Monochorionic twins are subjected to specific complications which originate in either imbalance or abnormality of the single placenta serving two twins. This unequal placental sharing can cause complications including twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), selective intrauterine growth restriction or twin reversed arterial perfusion sequence (TRAP). Monochorionicity also makes the management of these specific complications as well as that of a severe malformation in one twin hazardous since the spontaneous death of one twin exposes the co-twin to a risk of exsanguination into the dead twin and its placenta. The latter is responsible for the death of the co-twin in up to 20% of the cases and in ischemic sequelae in about the same proportions in the survivors. Although the symptoms of all these complications are very different, the keystone of their management comes down to either surgical destruction of the inter-twin anastomoses on the chorionic plate when aiming at dual survival or selective and permanent occlusion of the cord of a severely affected twin aiming at protecting the normal co-twin. This can be best achieved by fetoscopic selective laser coagulation and bipolar forceps cord coagulation respectively.

From monster to twin reversed arterial perfusion: a history of acardiac twins

A human being born without heart and head, i.e., the acardius/acranius malformation, has been described since antiquity. Superstition and fear made it a mystical disorder, a sign of God's wrath. The inquisition ruled that acranic infants should not be baptized and located the soul in the brain. Acardia was not associated with twin gestation until the reports of Mery in 1720 and Winslow in 1740. In 1850, Meckel identified the pathogenetic mechanism as reversed perfusion due to large arterio-arterial and veno-venous anastomoses; he believed the heart would fail to develop or arrest during development, and the acardiac fetus would be maintained by arterial perfusion from the pump twin. In 1859, Claudius articulated that after normal initial development, the heart degenerates when reversed flow in the aorta leads to thrombosis. Today, it is assumed that both mechanisms may exist. With the advent of prenatal ultrasound diagnosis and radiofrequency ablation of the acardiac twin's circulation, it became possible to save the pump twin.

Placental pathology in trap sequence: clinical and pathogenetic implications

Twin reversed arterial perfusion sequence (TRAP) resulting in an acardiac twin is a rare occurrence. Acardia requires the presence of arterial-arterial anastomosis, with retrograde perfusion of poorly oxygenated blood from the normal twin to the acardiac twin, venous-venous anastomosis carrying blood back from the acardiac to the normal twin, and circulatory failure of the acardiac twin. Although vascular anastomoses in cases of TRAP have been well described, there is little published literature on the microscopic changes in the placenta in TRAP sequence. We report a case of monochorionic monozygotic twins with an acardiac twin, large arterial-arterial anastomosis, and direct continuity of the umbilical cord veins. The placenta showed villous immaturity, striking villous calcifications, and extensive fetal thrombotic vasculopathy of the umbilical vein of the donor twin and the chorionic plate vessels. Thrombi in the umbilical vessels of the acardiac twin have been reported, and trombi in donor twin organs have been seen after fetal demise in utero. But to our knowledge there is no previously reported thrombi in the donor twin umbilical vessels or the chorionic plate veins. This may have implications not only as a possible factor in the etiology of TRAP, but also and more important as a possible risk factor for thrombotic events in the donor twin. Further studies with clinico-pathological correlation are needed to explore this issue.

Selective cord coagulation in acardiac twins

The twin reverse arterial perfusion (TRAP) sequence is a serious complication of monochorionic multiple pregnancies in which the affected twin is reversely perfused from the healthy co-twin, resulting in severely abnormal or absent cardiac development, severe malformations, and massive hydrops fetalis. The acardiac twin threatens the survival of the pump twin either by increasing the risk of congestive cardiac failure or by the development of polyhydramnios, preterm premature rupture of membranes, preterm labour and premature delivery. A wide spectrum of surgical interventions has been applied in the management of TRAP; however, because of the rarity of this condition and the heterogeneity of its presentation, no single technique has been shown to be unequivocally optimal. In our experience, fetoscopic laser coagulation of the placental vascular anastomoses or the umbilical cord of the acardiac twin, with the possibility of applying bipolar forceps as an additional minimally invasive surgical technique, offers an effective treatment option in the management of the TRAP sequence; this treatment has a survival rate of 80%, and 67% of pregnancies with surviving pump twins go beyond 36 weeks of gestation without further complications.

Acardiac twin fetus with severe hydrops fetalis and bilateral talipes varus deformity

Twin reversed-arterial-perfusion syndrome (TRAPS) is a rare complication of monochorionic twin pregnancies. TRAPS is characterized by the hemodynamic dependence of a "recipient" twin from a "pump" twin. The "recipient" twin exhibits lethal abnormalities, such as acardia and acephaly. Circulatory failure of the normal twin derives from the existence of arterio-arterial and veno-venous anastomoses within the placenta that allow retrograde perfusion of the acardiac twin by blood coming from the normal twin. Acardiac twinning is the most extreme manifestation of the twin-twin transfusion syndrome. This occurs in 1 in 100 monozygotic twin pregnancies and 1 in 35,000 births. We report a case of diamnionic monochorionic female twins in which the acardiac twin demonstrated severe hydrops fetalis and bilateral talipes varus deformity. Cesarean section was performed on a 27-year-old hypertensive gravida 2, para 1 mother for fetal indications at 32 6/7 weeks gestation. The acardiac fetus had a two-vessel umbilical cord measuring 43.5 cm in length and 0.8 cm in diameter. The proximal end inserted into the root of the normal twin's umbilical cord in an acute angle forming a "v" close to the placental disc. Structures rostral to the thorax were absent except for a round mass of flesh with three small buds in place of the head and neck, and bilateral upper extremities. Only the kidneys, right adrenal, small and large intestine, and rudimentary urinary bladder were present. Both feet demonstrated talipes varus deformity. The fetus was severely hydropic. The subcutaneous fat measured 4.5 cm in maximum thickness. The normal twin had a protracted course complicated with respiratory distress syndrome, moderate secundum atrial septal defect with left to right shunt, and thrombocytopenia of prematurity. The baby was eventually discharged after approximately 1 month. At the time of this report, 5 months postpartum, the neonate is growing and developing normally. To our knowledge, this is the first report of severe hydrops fetalis and talipes varus deformity in an acardiac twin.

Modeling Acardiac Twin Pregnancies

Acardiac twin pregnancies are a rare but severe complication of monochorionic twinning, where the acardiac twin lacks cardiac function but nevertheless grows during pregnancy because it is perfused by the pump twin through a set of placental arterioarterial and venovenous anastomoses. Because the acardiac twin's body is only perfused by the pump twin's arterial blood, acardiac twins have reduced blood oxygen saturation (SO(2)) levels. Furthermore, the pump twin has reduced blood oxygen saturation because the anastomoses merge the blood of the two twins. We suggested that angiogenesis from hypoxia mediated neovascularization increases the capillary density in the acardiac twin and causes a continuously decreasing vascular resistance of the acardiac body. The pump twin therefore has a continuously increasing cardiac output and decreasing oxygen saturation, which may cause a vicious circle of increasing levels of pump twin complications, often leading to intrauterine fetal death. Our aim in this article was twofold. First, to summarize our previous modeling work of acardiac twin pregnancies, and add an estimate of the capillary density in mammals at different levels of SO(2) from a literature search on angiogenesis related to SO(2), Hypoxia Inducible Factor, and Vascular Endothelial Growth Factor. Second, to speculate that combination of these efforts and our most recent model of monochorionic twin pregnancies and twin-twin transfusion syndrome may result in an improved computational model for acardiac twin pregnancies, aimed at identifying early clinical prognostic markers for pump twin complications.

Treatment of twin reversed arterial perfusion sequence by septostomy and amniodrainage: a case report

INTRODUCTION

An acardiac fetus is the most severe malformation seen in humans. It is an extremely rare complication, occurring in approximately 1% of all monozygotic twin gestations, with an incidence of about 1 in 35,000 births. This malformation happens as a result of the syndrome of reversed arterial perfusion of the acardiac twin from the other normal fetus (pump twin), due to the presence of arterio-arterial anastomoses in a monochorionic placenta. Several obstetric and perinatal complications have been associated to this anomaly and several treatments have been proposed to reduce the morbimortality of the pump twin. There's no report in MEDLINE about the treatment of twin gestations with acardiac fetus through septostomy.

CASE REPORT

The present article reports a case of reversed arterial perfusion sequence complicated by polyhydramnios diagnosed at 19th week of pregnancy, treated with septostomy and serial amniodrainage.

DISCUSSION

This case presented it demonstrate favorable development of the gestation, with labor happening at 35 weeks gestation and pump twin presenting good vitality conditions. In cases with no major factors of bad prognosis, septostomy combined with amniodrainage could be an interesting therapeutic option for a safe and efficacious management of selected cases of TRAP sequence.

Management of Multiple Pregnancy

Over the past 20 years, the number and rate of multiple births have dramatically increased in the United States. The rise in multiple births is mainly attributable to the increased use of ovulation-inducing drugs and the newly developed assisted reproductive technologies such as in vitro fertilization. Multifetal gestation is associated with an increased risk of perinatal morbidity and mortality. Multiple births account for an increasing percentage of low-birth-weight infants, preterm births, and infant mortality. In this article, the unique complications of multiple gestation and their management are reviewed. Also, selective termination and multifetal reduction in multiple gestation are discussed.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader should be able to describe the effects of the rising rate of multiple pregnancies on perinatal morbidity and mortality, to recall the complications of diagnosing and treating abnormalities of multiple pregnancies, to list the multiple severe complications associated with multiple gestations, and to describe the difficulty in managing these complications.

Increasing cardiac output and decreasing oxygenation sequence in pump twins of acardiac twin pregnancies

An acardiac twin pregnancy is a rare but serious complication of monochorionic twinning and consists of an acardiac twin and a pump twin. The acardiac twin is a severely malformed fetus that lacks most organs, particularly a heart, but grows during pregnancy because it is perfused by the developmentally normal pump twin via a set of arterioarterial and venovenous placental anastomoses. Pump twins die intrauterine or neonatally in about 50% of the cases. Because the effects of an acardiac mass on the pump twin's development are incompletely known, methods for outcome prognosis are currently not available. We sought to derive simple relations for the pump twin's excess cardiac output and decreased oxygenation and to use available clinical cases for a preliminary test of the model. As a method, we used a theoretical flow model to represent the fetoplacental circulation of an acardiac twin pregnancy and estimated blood deoxygenation and reoxygenation following perfusion of the two bodies and placentas, respectively. The results show the pump twin's excess cardiac output and decrease of venous oxygen saturation to depend on the ratio of pump twin to acardiac twin umbilical blood flow, whose ratio can be measured by ultrasonography. The clinical cases show a decreasing umbilical flow ratio with gestation. In conclusion, prospective serial study is necessary to test whether measurement of umbilical flow ratios allows monitoring the pump twin's pathophysiologic development, possibly resulting in a guideline for prognosis of pump twin survival.