Doppler sonographic demonstration of arterio-venous anastomosis in monochorionic twin gestation

Twin Anemia-Polycythemia Sequence (TAPS): From Basic Research to Clinical Practice

Twin pregnancy is associated with an increased risk of perinatal and maternal complications, and early establishment of the chorionicity type defines this risk. In monochorionic (MC) pregnancies, the fetuses share the same placental mass and exhibit vascular anastomoses crossing the intertwin membrane, and the combination and pattern of anastomoses determine the primary clinical picture and occurrence of future complications. Twin Anemia-Polycythemia Sequence (TAPS) was first described in 2006 after fetoscopic laser surgery in twin-to-twin transfusion syndrome (TTTS) twins, and in 2007, the first spontaneous cases were reported, recognizing TAPS as an individualized vascular identity in fetofetal transfusion syndromes. There are two types of TAPS: spontaneous (3-5%) and iatrogenic or postlaser (2-16%). TAPS consists of small diameter arteriovenous anastomoses (<1 mm) and low-rate, small-caliber AA anastomoses in the absence of amniotic fluid discordances. There are certain antenatal and postnatal diagnostic criteria, which have progressively evolved over time. New, additional secondary markers have been proposed, and their reliability is being studied. The best screening protocol for TAPS in MC twins is still a matter of debate. This review provides a survey of the relevant literature on the epidemiology, vascular pathophysiology, underlying hemodynamic factors that regulate mismatched vascular connections, and diagnostic criteria of this condition. The aim is to increase awareness and knowledge about this recently identified and frequently unrecognized and misdiagnosed pathology.

Additional benefits of three-dimensional ultrasound for prenatal assessment of twins

Three-dimensional ultrasound (3DUS) may provide additional information for prenatal assessment of twins. It may improve the diagnostic confidence of dating, nuchal translucency (NT) and chorionicity assignment in twin pregnancies. The "virtual 3DUS placentoscopy" can guide selective fetoscopic laser photocoagulation (SFLP) to treat twin-twin transfusion syndrome (TTTS). Volumetric assessment of the dysmorphic acardiac twin with the Virtual Organ Computer-aided Analysis (VOCAL) software is more accurate than the conventional ultrasound measurement. Twin anemia polycythemia (TAP) sequence and selective intrauterine growth restriction (sIUGR) may be clinically monitored with 3DUS placental volume (PV) and power Doppler vascular indices. Congenital anomalies are more common in twins. Evaluation of fetal anomalies with 3DUS could assist perinatal management. The 3DUS power Doppler can provide a better understanding of true and false umbilical cord knots, which are commonly found in monoamniotic (MA) twins. Single demise in monochorionic (MC) twin pregnancies can cause severe neurologic morbidity in the surviving co-twin. Prenatal prediction of brain injury in the surviving co-twin with unremarkable neurosonographic examination is difficult. The 3DUS power Doppler may aid in prenatal detection of subtle abnormal cerebral perfusion. Prenatal assessment of conjoined twins with 3DUS is important if emergency postnatal surgical separation is anticipated. There is no significant additional advantage in using real-time 3DUS to guide prenatal interventions. Assessment of the cervix and pelvic floor during twin pregnancies is enhanced with 3DUS. Due to lack of high-quality studies, routine prenatal 3DUS in twin pregnancies needs to be balanced with risks of excessive ultrasound exposure.

Noninvasive high-intensity focused ultrasound treatment of twin-twin transfusion syndrome: A preliminary in vivo study

We investigated the efficacy, maternofetal responses, and safety of using high-intensity focused ultrasound (HIFU) for noninvasive occlusion of placental vasculature compared to sham treatment in anesthetized pregnant sheep. This technique for noninvasive occlusion of placental vasculature may be translatable to the treatment of conditions arising from abnormal placental vasculature, such as twin-twin transfusion syndrome (TTTS). Eleven pregnant sheep were instrumented with maternal and fetal arterial catheters and time-transit flow probes to monitor cardiovascular, acid-base, and metabolic status, and then exposed to HIFU (n = 5) or sham (n = 6) ablation of placental vasculature through the exposed uterine surface. Placental vascular flow was occluded in 28 of 30 targets, and histological examination confirmed occlusion in 24 of 30 targets. In both HIFU and sham exposures, uterine contact reduced maternal uterine artery flow, but delivery of oxygen and glucose to the fetal brain remained normal. HIFU can consistently occlude in vivo placental vessels and ablate blood flow in a pregnant sheep model. Cardiovascular and metabolic fetal responses suggest that the technique is safe in the short term and potentially translatable to human pregnancy.

What-and why-the pathologist should know about twin-to-twin transfusion syndrome

Approximately 20% of all twin pregnancies are monochorionic. Between 9% and 15% of all monochorionic twin gestations are complicated by severe chronic twin-to-twin transfusion syndrome (TTTS), characterized by a gradual shift of blood volume from the donor twin to the recipient twin through placental vascular connections [1 - 3] . The prognosis of severe, untreated chronic TTTS diagnosed in midtrimester fetuses is extremely poor, with mortality rates exceeding 70% [4] . Since publication of the results of the Eurofoetus trial in 2004, laser photocoagulation of the intertwin anastomoses has become accepted as the optimal first-line therapy for severe TTTS diagnosed before 26 weeks of gestation. While laser treatment of vascular communications was initially limited to selected fetal treatment centers, its increasingly widespread use has resulted in the exposure of more pathologists, even in less specialized institutions, to laser-treated placentas. Furthermore, the surge in laser coagulation has revived the general medical, scientific, and public interest in the placental and choriovascular findings in monochorionic twin placentas. The pathologist's understanding of the pathophysiology of TTTS and of TTTS-associated placental pathology, including the findings related to laser ablation of the anastomoses, can be of great benefit to the involved obstetric/neonatal/surgical team and, ultimately, to the patients. In this review, we summarize the current knowledge of the placental contributions to TTTS and other complications of monochorionic twinning and describe the strengths and limitations of placental examination in these settings. It is our expectation that overviews such as this may serve as a template to generate consensus guidelines for standardized and evidence-based pathologic evaluation of monochorionic twin placentas.

Placentation in Multiple Births

Outcomes of multifetal pregnancy in prenatal life are markedly affected by chorionicity. Several disease processes are found in monochorionic (MC) twins that do not occur in dichorionic (DC) twins. Improvements in prenatal outcomes will depend on reliable first trimester diagnosis of chorionicity, allowing early monitoring for complications of MC placentation. Particular structures and functions of MC twin placentas affect outcomes and can be targeted for specific treatments, especially in twin-twin transfusion. The causes of severe DC twin fetal growth discordance are clarified. In post-natal life, zygosity is a determining effect in genetic predisposition to many chronic diseases, including neoplasia. Few MC twins know that they are monozygotic (MZ). Few twin researchers realize that MZ twins may be genetically discordant. Abandonment of the word “identical” for MZ twins would assist in clarifying these issues of zygosity, concordance and discordance.

The Role of Ultrasound in Multiple Pregnancy

The advances in reproductive technologies have changed the demographics of multifetal pregnancies. In the first trimester, ultrasound allows to diagnose the number of multiples, chorionicity and amnionicity, the presence or absence of nuchal translucency, early growth discordance, severe malformations and the origin of activities and contacts between multiples. In the second and third trimester, the opportunity to examine the cervix by transvaginal ultrasound should not be missed to detect the risk of premature delivery. Ultrasound is essential for the early grading and treatment of twin-to-twin transfusion syndrome (TTTS), the diagnosis of malformations and growth disturbances. Doppler velocimetry has proven to be able to reduce perinatal mortality in twin pregnancies. Finally, ultrasound is used for the detection of the position of multiples and the decision of the optimal route of delivery. This is of main importance in delayed interval delivery and expectant management of multifetal pregnancies and early cervical dilatation.

Guide wire assisted catheterization and colored dye injection for vascular mapping of monochorionic twin placentas

Monochorionic (MC) twin pregnancies are associated with significantly higher morbidity and mortality rates than dichorionic twins. Approximately 50% of MC twin pregnancies develop complications arising from the shared placenta and associated vascular connections. Severe twin-to-twin syndrome (TTTS) is reported to account for approximately 20% of these complications. Inter-twin vascular connections occur in almost all MC placentas and are related to the prognosis and outcome of these high-risk twin pregnancies. The number, size and type of connections have been implicated in the development of TTTS and other MC twin conditions. Three types of inter-twin vascular connections occur: 1) artery to vein connections (AVs) in which a branch artery carrying deoxygenated blood from one twin courses along the fetal surface of the placenta and dives into a placental cotyledon. Blood flows via a deep intraparenchymal capillary network into a draining vein that emerges at the fetal surface of the placenta and brings oxygenated blood toward the other twin. There is unidirectional flow from the twin supplying the afferent artery toward the twin receiving the efferent vein; 2) artery to artery connections (AAs) in which a branch artery from each twin meets directly on the superficial placental surface resulting in a vessel with pulsatile bidirectional flow, and 3) vein to vein connections (VVs) in which a branch vein from each twin meets directly on the superficial placental surface allowing low pressure bidirectional flow. In utero obstetric sonography with targeted Doppler interrogation has been used to identify the presence of AV and AA connections. Prenatally detected AAs that have been confirmed by postnatal placental injection studies have been shown to be associated with an improved prognosis for both twins. Furthermore, fetoscopic laser ablation of inter-twin vascular connections on the fetal surface of the shared placenta is now the preferred treatment for early, severe TTTS. Postnatal placental injection studies provide a valuable method to confirm the accuracy of prenatal Doppler ultrasound findings and the efficacy of fetal laser therapy. Using colored dyes separately hand-injected into the arterial and venous circulations of each twin, the technique highlights and delineates AVs, AAs, and VVs. This definitive demonstration of MC placental vascular anatomy may then be correlated with Doppler ultrasound findings and neonatal outcome to enhance our understanding of the pathophysiology of MC twinning and its sequelae. Here we demonstrate our placental injection technique.

Mise en évidence des anastomoses vasculaires par la vélocimétrie doppler dans les grossesses gémellaires monochoriales. Revue de la littérature à propos de trois cas

Three cases of intermittent absent end-diastolic and reversed end-diastolic flow velocity (A/REDV) are reported in the proximal umbilical artery of the growth-retarded twin in monochorionic twin pregnancies. This typical doppler velocimetric pattern has been related to arterio-arterial anastomoses in two cases of intra-uterine growth retardation and in one case of twin-twin transfusion syndrome. According to the literature, superficial arterio-arterial anastomoses may be detected by doppler colour velocimetry in 75 to 85% of cases, while identification of arteriovenous connections is more difficult to be documented in vivo (50% of cases in experienced hands). The role of superficial vascular anastomoses, either arterio-arterial or venovenous, and that of deep arteriovenous communications is now well documented in the main complications of monochorionic pregnancies, particularly for twin-twin transfusion syndrome, intrauterine growth retardation, intrauterine fetal death and acardiac twins.

Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy

OBJECTIVES

To revalidate the detection technique for arteriovenous anastomoses in an unselected group of monochorionic twins, and to make recommendations about its applicability for more widespread use.

METHODS

Women with monochorionic diamniotic (MCDA) twins were recruited and underwent placental mapping by color Doppler ultrasound. Images of placental maps showing the location and type of anastomoses were saved as digital video clips. After delivery, dye injection study of all the placentas was performed to delineate the site and type of anastomoses. A digital photograph of each injection study was taken and saved. The antenatal ultrasound images and postnatal dye injection studies were compared.

RESULTS

18 sets MCDA twins were evaluated. In 3 cases there was evidence of twin-to-twin transfusion syndrome. Dye injection of 18 placentas revealed 21 arterio-arterial anastomoses (AAA), 21 arteriovenous anastomoses (AVA) and 4 veno-venous anastomoses (VVA). Of these, 10 (48%) AAAs and 5 (24%) AVAs were detected antenatally by color Doppler. In all cases, where an AVA was detected, the placenta was located anteriorly.

CONCLUSION

Antenatal detection of AVA was feasible when the placenta was located anteriorly, but proved difficult in posteriorly situated placentas.

What--and why--the pediatric surgeon should know about twin-to-twin transfusion syndrome

Abstract Endoscopic laser ablation of placental vessels is the most commonly performed fetal operation today. Herein, we review the pathophysiology of twin-to-twin transfusion syndrome and the challenges of its treatment. Pediatric surgeons, with their knowledge of fetal and congenital pathology, and their technical expertise with minimally invasive surgery, can be of great benefit to the patient and the medical team.

Limited Prognostic Value of a Staging System for Twin-to-Twin Transfusion Syndrome

OBJECTIVE

Severe twin-to-twin transfusion syndrome (TTTS) is usually classified according to a staging system (I-V) based on ultrasonographic findings of polyhydramnios in the recipient, oligohydramnios in the donor, the presence or absence of the donor's bladder, Doppler waveform changes and (impending) hydrops. Stage correlates with the severity of disease, and it is assumed that, without intervention, severe TTTS will evolve in succession from stage I to stage V (fetal demise). However, this progression has not been validated in longitudinal studies. Herein, we report on the natural progression of severe TTTS in a cohort of patients from a regional Fetal Treatment Program.

METHODS

Eighteen patients with severe TTTS, diagnosed between 15 and 25 weeks of gestation, were managed over a 28-month period. Data were collected until delivery, endoscopic surgical intervention or dual fetal demise. Patients were evaluated at least once a week. Stage, estimated fetal weight, percent recipient/donor body weight discordance and survival were recorded.

RESULTS

The present study represents a total follow-up of 108 patient-weeks. Of 90 week-to-week evaluations, 65 showed no change in stage; 11 showed downstaging (by more than 1 stage in 3, or 27%), and 13 showed upstaging (by more than 1 stage in 8, or 62%). Nine patients (all stage II or above) underwent endoscopic laser ablation. Overall survival was 67%, and survival of at least 1 twin occurred in 78% of pregnancies. Weight discordance between the donor and recipient did not predict outcome.

CONCLUSION

The current staging system for severe TTTS may not be helpful in predicting the direction, degree or speed of progression of the condition. Indications for intervention should remain stage-related, and not based on projected progression.

Stratégies de diagnostic prénatal et prise en charge des pathologies liées aux grossesses multiples

In the first trimester, ultrasound is crucial to screen for aneuploidies based on nuchal translucency, to diagnose major birth defects, and to establish chorionicity. Indeed prenatal diagnosis strategies as well as obstetrical management options are largely based on placental type. In the second trimester, maternal serum screening is not as effective, and ultrasound screening is more difficult in twins than in singletons. When a severe abnormality in found in one twin, selective termination of pregnancy may be considered. This technique is safe in dichorionic twins, but hazardous in monochorionic pregnancies. Selective termination in dichorionic twins is safer in the first trimester, underscoring the need for early prenatal diagnosis in twins. Monochorionic twin pregnancies carry specific risks, such as the twin-to-twin transfusion syndrome, which can be treated by endoscopic photo-coagulation of intertwin anastomoses in the severe early onset cases, or by amnioreduction in milder cases.

Complications of monochorionic twins

Sonography has made a dramatic impact on the obstetric management of complicated twin pregnancies. This is based in part on the ability to use prenatal US to diagnose syndromes and complications of MC twinning. All twin pregnancies are at high risk for perinatal morbidity and mortality compared with singleton gestations, but when one of the described complications is recognized, the difficulties in management are compounded dramatically. Despite the relative rarity of some of the entities described, it is vitally important to be familiar with these problems and their sonographic evaluation and diagnosis.

Understanding twin-twin transfusion syndrome: role of Doppler ultrasound

The high risks of monochorionic (MC) twin gestations are largely related to the vascular anatomy of the shared placentae and the presence of intertwin vascular connections. These anastomoses are implicated in twin-twin transfusion syndrome and co-twin sequelae after intrauterine death of one twin. Twin-twin transfusion syndrome is the most common complication of MC twinning. Obstetrical sonography, with the use of Doppler techniques, can be used to assess these high-risk pregnancies and to interrogate the vascular connections in the shared placentae. The information obtained can improve our understanding of the pathophysiology of syndromes that complicate these pregnancies and may help inform obstetrical management.

First trimester twin-to-twin transfusion syndrome in a trichorionic quadruplet pregnancy--a diagnostic challenge

We report the prenatal diagnosis of twin-to-twin transfusion syndrome (TTS) at 11 weeks' gestation. The diagnosis was made in a trichorionic quadruplet pregnancy which was conceived after in vitro fertilization and intracytoplasmic sperm injection for male subfertility and transfer of 3 embryos. Growth discordance, oligo/polyhydramnios and abnormal arterial and venous Doppler flows were demonstrated in 2 monochorionic fetuses, while the remaining 2 dichorionic fetuses were unremarkable. Selective fetocide of the donor by intracardiac injection of potassium chloride was followed by the spontaneous demise of the recipient. The pregnancy course remained uneventful until 32 weeks of gestation when the patient developed preterm labor. Two healthy preterm babies were delivered by cesarean section. The diagnostic problems of this early manifestation of TTS are discussed.

Does amniotic fluid volume affect fetofetal transfusion in monochorionic twin pregnancies? Modelling two possible mechanisms

Clinical evidence suggests that increased amniotic fluid volume due to polyhydramnios increases placental vascular resistance. We have sought to model the possible effects of an increased amniotic fluid volume on the net fetofetal transfusion in monochorionic twin pregnancies. We wanted to compare these effects with the results of previous simulations, which aimed to explain why the twin-twin transfusion syndrome (TTTS) placentas more often include bidirectional arteriovenous (AV) rather than AV plus arterioarterial (AA) anastomoses. We extended our mathematical model of TTTS by simulating two different mechanisms that increase the placental vascular resistance as a consequence of polyhydramnios. First, there is an increase in the placental capillary resistance and hence in deep AV and opposite AV (denoted as VA) resistances due to polyhydramnios. Second, there is an increase in the resistance of chorionic veins due to polyhydramnios, assuming that these veins act as Starling resistors. We then simulated the effects of polyhydramnios on different placental anastomotic patterns. The results were as follows. In the first mechanism (polyhydramnios affects AV-VA resistances), an increased amniotic fluid volume hardly affected bidirectional AV, but slightly decreased fetofetal transfusion in AV plus AA anastomoses. However, for these effects to change the natural development of the pregnancy, polyhydramnios needed to persist for approximately 4 weeks, and by comparing the effects of polyhydramnios with the effects of amnioreduction, amnioreduction was more beneficial for normalizing the donor amniotic fluid volume. Therefore, these beneficial effects due to polyhydramnios have no practical clinical significance. In the second mechanism (Starling resistor for chorionic veins), polyhydramnios slightly increased fetofetal transfusion and hence slightly increased TTTS severity in bidirectional AV and AV plus VV, but did not affect AV plus AA anastomoses. In conclusion, we hypothesize that the simulated effects of polyhydramnios are not the primary cause of the fact that TTTS placentas more often include bidirectional AV than AV plus AA anastomoses. Rather, the more likely explanation is the previously identified larger range of AA than VA anastomotic diameters that adequately compensate for the effects of the AV.

Neuromaturation of multiples

Etiology of preterm birth and degree of maturation are the primary determinants of a preterm infant's survival and complications. Multiple gestation increases the likelihood of preterm birth but its influence on rate of maturation or complications of prematurity has been controversial, primarily because of confounding variables (e.g. race, aetiology of preterm delivery, degree of prematurity and pregnancy complications). Very low birthweight preterm multiples have virtually the same rates of neonatal mortality, complications and neuromaturation as preterm singletons of the same gestational age. There is no advantage of delivering twins or higher order multiples before 30 weeks gestation, unless a fetus decompensates in utero. Survival improves for near term intermediate-size preterm multiples while intrauterine growth decelerates and placental and fetal neuromaturation accelerate. These data and the high fetal death rate at term support delivery of multiples as soon as there is fetal lung maturity, and consideration of elective delivery of twins at 35-38 weeks gestation and triplets at 33-35 weeks gestation.

Prenatal diagnosis for multiple pregnancies

In multiple pregnancies, first trimester ultrasound is crucial to diagnose chorionicity, to detect major structural defects, and to screen for chromosomal abnormalities based on nuchal translucency measurement. The efficacy of nuchal translucency measurement screening in twins might be improved when combined with first trimester maternal serum screening. In twins as in singletons, the risk of fetal loss attendant to chorionic villi sampling and to amniocentesis are similar. When an invasive procedure is indicated in twins, chorionic villi sampling has, over amniocentesis, the advantage of allowing selective termination to be performed in the first trimester, when the procedure related risk of miscarriage is minimal. It has the disadvantage of leading to ambiguous results in up to 2% of cases. While chorionic villi sampling is the choice technique in pregnancies at very high risk, amniocentesis is still indicated in cases at more moderate risk. In monochorionic pregnancies, selective termination can now be performed using a variety of techniques including bipolar or monopolar cord coagulation, and, in acardiac twins, alcohol ablation. However, selective termination remains more hazardous in monochorionic than in dichorionic pregnancies. The outcome of the twin-to-twin transfusion syndrome has been substantially improved by laser photocoagulation of placental shunts and by amniodrainage, but randomized trials are needed to establish the optimal therapeutic strategy, and further pathophysiologic research might result in new treatments.

Monochorionic twins and twin-twin transfusion syndrome: the protective role of arterio-arterial anastomoses

Unidirectional arterio-venous (AV) anastomoses often result in twin-twin transfusion syndrome (TTTS). Additional oppositely directed anastomoses may compensate for the circulatory imbalance and either prevent, delay the onset, or moderate the severity of TTTS. Intuitively, higher pressure gradient, oppositely-directed AV anastomoses (indicated as VA) would be expected to compensate better for TTTS than lower pressure gradient arterio-arterial (AA) anastomoses. However, clinical evidence suggests AA anastomoses compensate more efficaciously, because virtually all non-TTTS monochorionic twin placentas have AAs (84 per cent), contrary to TTTS placentas, where only 30 per cent have an AA. We sought to explain this observation by comparing the capabilities of various size VA and AA anastomoses to compensate for the effects of the primary AV. As study design we used a previously developed mathematical computer model of TTTS to determine ranges of anastomotic vascular resistances which cause varying fetal and amniotic fluid discordances. Anastomotic resistances were related with the radii of their feeding vessels, using fractal geometry modelling to mimic the placental vascular tree, and various assumptions regarding arterial blood flow. The results were as follows. An AA anastomosis of equal size as the feeding artery of an AV or VA has a significantly smaller resistance. The primary AV anastomosis may be compensated by both VA as well as AA anastomoses. However, VA transfusion adequately compensates AV flow only for a small range of VA to AV vascular radius ratios. In contrast, AA transfusion compensates the AV flow for a much wider range of AA to AV vascular radius ratios. In conclusion, the wider range of AA than VA radii for adequate compensation of the AV explains the finding that an AA protects more frequently than a VA of similar size against the manifestations of TTTS. These results may possibly allow future risk stratification of monochorionic twins by non-invasive sonographic assessment of the size and type of anastomoses.

Placental vascular anastomoses visualized during fetoscopic laser surgery in severe mid-trimester twin-twin transfusion syndrome

The aim of this study was to describe the type and number of placental vascular anastomoses identified during fetoscopic laser coagulation in severe mid-trimester twin-twin transfusion syndrome (TTS). In 126 patients with severe TTS, undergoing fetoscopic laser coagulation between 16 and 25 weeks of gestation, the different types of placental anastomoses [arterio-venous (AV), arterio-arterial (AA) and veno-venous (VV)] were counted. In cases of AV anastomoses their direction was identified and four groups were defined: in group 1 there were only anastomoses shunting from donor to recipient. Group 2 consisted of placentae with more anastomoses shunting from donor to recipient than in the opposite direction, group 3 showed an equal number in both directions and in group 4 there were more anastomoses shunting from recipient to donor than in the opposite direction. In 9 cases (7 per cent) the anastomoses could not be clearly identified due to impaired visualization, leaving 117 cases for analysis. The median number of anastomoses found was 5 with a range from 1-14. In all cases AV anastomoses from donor to recipient were present, 36 cases (31 per cent) had also AA anastomoses and 14 cases (12 per cent) showed VV anastomoses. Regarding the direction of AV anastomoses, the results were as follows: there were 35 cases (30 per cent) in group 1, 52 cases (44 per cent) in group 2, 14 cases (12 per cent) in group 3 and 16 cases (14 per cent) in group 4. In 54 (46 per cent) placentae there was at least one thin anastomosis whose type was unclassifiable. There were no placentae showing AV anastomoses only from the recipient to the donor fetus. This study demonstrates that AV anastomoses are the prerequisite for the development of TTS in monochorionic placentae. The majority (74 per cent) of cases showed a higher number of AV anastomoses from donor to recipient than in the opposite direction. In approximately one third of placentae there are also AA anastomoses and the overall number of anastomoses seen and coagulated during fetoscopy is higher than reported in postnatal studies.

Freehand three-dimensional Doppler demonstration of monochorionic vascular anastomoses in vivo: a preliminary report

OBJECTIVES

To demonstrate the three-dimensional vascular anatomy of monochorionic placental anastomoses in vivo, both arterioarterial and arteriovenous.

DESIGN

Two-dimensional placental mapping techniques were used to locate arterioarterial and arteriovenous anastomoses. A freehand sweep was performed across the anastomotic site, and multiple images were stored to disk, at 17 Hz. These were then segmented to show only color information (vascular flow) using purpose-designed software (CQ analysis) and the files reconstructed into a three-dimensional volume, for multidirectional viewing and movie generation.

RESULTS

Both arterioarterial and arteriovenous anastomoses could be visualized in detail. Reconstruction of a dual volume of gray-scale and segmented color images allowed recreation of the vascular anatomy within the placental substance, as well as retention of the original directional flow information.

CONCLUSIONS

Detailed anastomotic anatomy can be demonstrated three dimensionally in vivo. Given the increasing evidence implicating various anastomotic configurations in pathological intertwin transfusion, this technique may prove useful in the antenatal assessment and treatment of monochorionic twin pregnancies.