Monoamniotic-versus diamniotic-monochorionic twin placentas: anastomoses and twin-twin transfusion syndrome

OBJECTIVE

The purpose of this study was to compare monoamniotic-monochorionic and diamniotic-monochorionic twin placentas and to estimate the incidence of twin-twin transfusion syndrome in monoamniotic-monochorionic twin pregnancies.

STUDY DESIGN

We analyzed the angioarchitecture and cord insertion distance in 24 monoamniotic-monochorionic and 200 diamniotic-monochorionic placentas.

RESULTS

Compared with diamniotic-monochorionic placentas, monoamniotic-monochorionic placentas had significantly more arterioarterial anastomoses (20/20 vs 159/200, respectively; P=.013), significantly less opposite arteriovenous anastomoses (10/20 vs 165/200, respectively; P=.002), similar venovenous anastomoses (6/20 vs 46/200, respectively; P=.323), and arteriovenous anastomoses (20/20 vs 187/200 respectively; P=.279) and significantly shorter umbilical cord distances (median [+/-SD], 5.0+/-6.9 cm vs 17.5+/-6.8 cm; P<.001).

CONCLUSION

Monoamniotic-monochorionic and diamniotic-monochorionic placentas have different anastomotic patterns. The (virtually) 100% incidence of arterioarterial anastomoses in monoamniotic-monochorionic placentas explains the reason that twin-twin transfusion syndrome rarely occurs in monoamniotic-monochorionic twin pregnancies and predicts that twin-twin transfusion syndrome manifestations are approximately 5 times less often recognized in monoamniotic-monochorionic pregnancies than in diamniotic-monochorionic pregnancies.

A case of TRAP sequence: acardiac twin

Monochorionic twinning contributes significantly to neonatal morbidity and mortality. The twin-twin transfusion syndrome complicates 5-35% of monozygotic twin pregnancies with monochorionic placentation. The most severe and a rare manifestation of this condition is acardiac twinning which is seen in 1 in 35,000 pregnancies. The acronym TRAP (Twin Reversed Arterial Perfusion) sequence is used to describe this condition. The acardiac twin does not survive while the mortality for the normal twin is about 50%. Proper timing of the delivery is of prime importance to survival of the normal fetus for which emphasis is placed on close sonographic monitoring for early antenatal diagnosis. We present such a case of TRAP sequence because of its rarity.

Renal tubular apoptosis in twin-to-twin transfusion syndrome

Twin-to-twin transfusion syndrome (TTTS) is caused by uneven shunting of blood between monochorionic twins, resulting in polycythemia in the recipient twin and growth restriction, anemia, and oliguria in the donor twin. Recent reports have described loss of proximal convoluted tubules in the kidneys of TTTS donor twins. In order to elucidate the pathogenesis of tubular deficiency in TTTS, we have reviewed the renal pathology in 25 twin pairs with autopsy-proven TTTS. Loss of differentiated proximal tubules, associated with atrophy of medullary tubules, was identified in 12/25 donor twins. In seven of these cases (all > 23-wk gestational age), the kidneys showed diffuse or partial tubular atrophy without evidence of cell death, similar to previously reported patterns. In five cases (all between 18- and 22-wk gestation), proximal and medullary tubules showed active injury characterized by markedly increased apoptosis, cell detachment, and intraluminal cell debris associated with calcifications. Tubular apoptosis tended to be more prevalent in donor fetuses with greater inter-twin body weight discordance, consistent with a more severe degree of TTTS. These results extend the spectrum of tubular alterations in TTTS to include an early stage of active apoptotic injury. The temporal distribution of injury patterns suggests that apoptotic injury of proximal and medullary tubules may be a precursor to partial or diffuse tubular atrophy. We speculate that the risk for development of tubular apoptosis in TTTS depends on the severity and timing of the hemodynamic imbalance, whereby early mid-trimester fetuses may be more vulnerable.

[Empirical report on acute twin-twin transfusion syndrome with single intrauterine death]

We report on a case of acute twin-twin transfusion syndrome in a twin pregnancy in the 26 th under primarily unclear conditions. On admission to the hospital, one fetus was not showing signs of life anymore, while the Doppler indices and CTG of the living fetus showed signs of acute distress. On the scan both fetuses showed adequate and symmetric growth as well as symmetric and normal amniotic fluid amounts, indicating a lack of typical signs for chronic twin-twin transfusion syndrome. The emergency cesarean section performed under the assumption of acute twin-twin transfusion syndrome, which unfortunately could not save the second twin, confirmed our suspected diagnosis.

Neuropathological features of the brain in acardius acormus

Acardia is the most severe complication in monozygotic twinning. Acardius acormus is an uncommon phenotype among acardias. We report on an acardius acormus using thorough gross and light microscopic examination of the brain. Neuropathological examination revealed a severely disorganized cerebral cortex, agenesis of cerebellum and brain stem, and undeveloped basal ganglia and thalamus. In particular, the cerebral cortex was characterized by no clear lamination, almost complete loss of neurons, extensive gliosis, angiogenesis and focal mineralization. Neurohistology of the acardius acormus clearly demonstrated two types of lesions: developmental arrest of the brain and hypoxic-asphyxic damage to the brain with reactive gliosis and angiogenesis. Both types of lesions may be induced by the same teratogen: early onset of persisting hypoxia due to a reversed arterial perfusion. The quality of the description contributes valuably to a better understanding of the basic mechanism underlying the acardius phenotype.

Placental types and twin-twin transfusion syndrome

OBJECTIVE

The purpose of this study was to assess the value of a proposed classification of monochorionic placenta in reference to twin-twin transfusion syndrome.

STUDY DESIGN

The placentas from laser-treated patients with twin-twin transfusion syndrome and from uncomplicated monochorionic pregnancies that were delivered between January 1997 and December 2000 were included in the study. Placentas were classified as type A (no anastomoses), type B (only deep anastomoses), type C (only superficial anastomoses), and type D (deep and superficial anastomoses). The number and type of anastomoses were documented in each placental type. The severity of twin-twin transfusion syndrome was assessed in stages, as previously described. The relationship between placental types and the development and severity of twin-twin transfusion syndrome was determined.

RESULTS

One hundred thirty-one placentas were examined. Twin-twin transfusion syndrome developed in 0% (0/4 placentas) of type A, in 100% (85/85 placentas) of type B, in 5.6% (1/18 placentas) of type C, and in 79.17% (19/24 placentas) of type D placentas. An average of 4.17 (range, 1-11) vascular anastomoses was found. The mean number of superficial anastomoses was not different between patients with twin-twin transfusion syndrome and patients with no twin-twin transfusion syndrome (1.6 vs 1.71, respectively; P =.69, Student t test). The presence or absence of superficial anastomoses was not associated with differences in the severity of twin-twin transfusion syndrome.

CONCLUSION

This classification represents a practical approach to the surgical pathologic assessment of vascular anastomoses in monochorionic placentas, with a strong clinical correlation. It also allows for the clarification of the relationship between superficial anastomoses and twin-twin transfusion syndrome.

Umbilical cord cyst in a monochorionic twin pregnancy: an experiment of nature for the treatment of twin-twin transfusion syndrome

A patient with a monochorionic twin pregnancy developed signs of twin-twin transfusion syndrome from 18 weeks of gestational age. At 23 weeks, an umbilical cord cyst and absent diastolic umbilical artery flow were noted in the donor twin. The pregnancy progressed uncomplicated until term and resulted in vaginal delivery of 2 healthy male babies at 38 weeks of gestational age. We hypothesize that the compression on the umbilical arteries of the donor twin by the umbilical cord cyst has resulted in a partial "compensation" of the twin-twin transfusion phenomenon.

The placenta in multiple pregnancy: outstanding issues

The present paper reviews the placental development in multiple gestations and highlights the twin-to-twin transfusion syndrome, its recognition and possible therapy, and some of the consequences of fetal death of one twin. It presents data on discordance for structural anomalies in monozygotic twins. These aspects are discussed with respect to their possible pathogenetic origins.

[Pathophysiology and therapeutic possibilities in twin-to-twin transfusion syndrome]

INTRODUCTION

Twin-to-twin transfusion syndrome is a threatening consequence of monochorionicity. Without therapeutic intervention it has approximately a 100% mortality rate, but due to therapeutic efforts it improved dramatically to about 20-50% mortality. It is caused by arteriovenosus anastomoses within the placenta, that causes hormonal changes, polyhydramnios, hypertension of the recipient and weight discordance.

AIMS

Detection of ultrasonographic and pathologic consequences of twin-to-twin transfusion syndrome.

PATIENTS AND METHODS

Ultrasonographic and pathologic findings of six twin pairs were analysed with the common feature of twin-to-twin transfusion syndrome.

RESULTS

Ultrasonographic and pathologic results were suggestive for fetal hypertension in all recipients and pulmonary stenosis in four of them.

CONCLUSION

The prognosis of twin-to-twin transfusion syndrome can be improved significantly with serial amnioreduction, amniotic fenestration, laser ablation of connecting vessels or selective fetocidium. Proper therapy prevents the development of the serious clinical and pathological consequences of twin-to-twin transfusion syndrome.

Rapid onset of severe twin-twin transfusion syndrome caused by placental venous thrombosis

We report a case of rapid onset of severe twin-twin transfusion syndrome (TTTS) at 25 weeks gestation in a monochorionic twin pregnancy that was uneventful before that time. Thrombosis of a main venous branch draining several arteriovenous (AV) anastomoses to the donor changed the previous hemodynamic balance that existed between multiple bidirectional AV anastomoses. The opposing AVs became hemodynamically uncompensated and, despite amnioreductions, severe TTTS developed. At 27 weeks a cesarean section was performed because of worsening cardiotocography parameters of both fetuses. Birth weights were 750 and 1840 g, and initial hemoglobin concentrations were 9.2 and 13.4 mmol/liter for donor and recipient, respectively. The recipient twin died 5 months later of an ischemic, necrotic, and perforated small intestine due to a thrombosed superior mesenteric artery. The donor is well at 2.5 years. No abnormalities in several factors associated with thrombophilia, including factor V Leiden mutations, were found in the parents.

Perinatal hepatic infarction in twin-twin transfusion

We report a case of a twin pregnancy which was complicated by a twin-twin transfusion in which the recipient twin was noted to have an intra-abdominal echogenic mass. This twin died at two days of age of hepatic infarction. The donor twin was healthy at birth, at thirty weeks' gestation, and did not have any subsequent problems. Fetal intra-abdominal echogenicity may be a marker of hepatic infarction.

Intrauterine left chamber myocardial infarction of the heart and hydrops fetalis in the recipient fetus due to twin-to-twin transfusion syndrome

A rare complication of twin-to-twin transfusion syndrome (TTTS) is described: myocardial infarction of the recipient fetus. Myocardial infarction and hydrops are considered to be consequences of hypertension in the recipient. No other organs were affected. Pathological signs of intrauterine hypertension were estimated by the thickness of vessel walls and signs of hypertrophied myocardial cells. In the heart of the recipient fetus there was a chronic myocardial infarction near the apex cordis on the anterior wall with an aneurysm 4x5 mm in diameter. Diagnosis was based on light microscopic examination. The poor myocardial systolic function resulted in hydrops. Since the mother was administered beta sympathomimetics in therapeutic doses the contribution of the drug to the myocardial infarction is uncertain, but we would like to suggest this as a possible adverse effect in TTTS. The present case is the first reported myocardial infarction in connection with the syndrome.

[Acute Renal Failure in Twin-to-Twin Transfusion Syndrome: Differential Diagnosis]

In the differential diagnosis of acute renal failure in Newborns prerenal, renal and postrenal causes must be considered. Additionally, in twin-to-twin transfusion syndrome especially the donor can suffer from acute renal failure caused by longterm intrauterine hypoperfusion of the kidneys resulting in severe retardation of renal development.

Demonstration of placental vascular anatomy in monochorionic twin gestations

Invasive treatment modalities for severe chronic twin-to-twin transfusion syndrome (TTTS), such as fetoscopic laser coagulation of communicating vessels, have revived the need for detailed studies of placental angioarchitecture. We describe a practical placental vascular injection technique using alcohol-resistant tissue-staining dyes. Injection of color-coded gelatin-dye mixtures effectively delineated the intertwin vasculature, and allowed unequivocal macroscopic classification of vascular communications as artery-to-artery, vein-to-vein, or deep artery-to-vein anastomoses. The existence of deep artery-to-vein anastomoses was further confirmed by light microscopic demonstration of venous dye of one twin and arterial dye of the opposite twin within the same stem villus. Furthermore, the injection technique allowed determination of the caliber of the anastomoses, the direction of the artery-to-vein anastomoses, and the relative vascular territory of each twin. Documenting the vascular communications in monochorionic twin placentas with and without TTTS may enhance our understanding of the pathogenesis of chronic TTTS. Correlating the anastomotic patterns and location of the laser coagulation scars with post-ablation outcome will aid in the design of rational therapeutic methods for this often lethal condition.

Preoperative planning with magnetic resonance imaging and computerized volume rendering in twin-to-twin transfusion syndrome

Our purpose was to illustrate the feasibility of preoperative planning with magnetic resonance imaging, 3-dimensional reconstruction, and volume-rendering techniques in twin-to-twin transfusion syndrome treated by endoscopic laser ablation of communicating vessels. After ultrasonographic determination of the syndrome and the indications for intervention, 2 patients with an anterior placenta underwent magnetic resonance imaging without the need for maternal or fetal sedation. Raw image data were downloaded into a desktop computer and manipulated with 3-dimensional reconstruction, volume rendering, and surgical navigation software. In both patients a virtual rendering of the fetuses, placenta, and uterus could be manipulated to expose all sides, demonstrate the location of the intertwin membrane, and plan the point of entry and curve of the endoscopic instruments. Preoperative planning and virtual surgical navigation in fetal surgery are now possible, as a result of shorter magnetic resonance imaging acquisition times and volume-rendering software. In this manner an entire virtual endoscopic fetal operation can be performed and fine-tuned before the actual procedure is to take place.

Twin-to-Twin Transfusion Syndrome Results From Dynamic Asymmetrical Reduction in Placental Anastomoses: A Hypothesis

Although placental vascular anastomoses between the fetoplacental circulations are ubiquitous in monochorionic twin pregnancies, the factors regulating their formation and maintenance are not understood. Increasing evidence implicates asymmetric anastomotic patterns in the aetiology of severe twin-to-twin transfusion syndrome (TTTS). The authors propose that anastomoses between placental circulations in monochorionic twins occur in a random manner at the embryological stage of connection of embryonic and extra-embryonic circulations. Placental expansion is then associated with random disruption of anastomoses and regression of their associated villus districts. TTTS develops as discordant loss of anastomoses results in asymmetrical flow resistance. Pregnancies with fetal growth concordance but discordant nuchal translucency at 10-14 weeks are at increased risk of developing subsequent severe TTTS because these clinical features indicate significant pressure differentials in the presence of a placentoplacental circulation, consistent with the presence of numerous, asymmetric anastomoses. However, since the anastomotic pattern is dynamic in the first half of pregnancy this hypothesis predicts that it will not be possible to devise a clinical test at 12 weeks that will predict with certainty the outcome of monochorionic twin pregnancies in relation to TTTS because this depends on random subsequent events.

Renal tubular dysgenesis-like lesions and hypocalvaria. Report of two cases involving indomethacin

We describe a case of twins with twin-to-twin transfusion syndrome (TTS) who were found to have renal tubular dysgenesis (TRD)-like lesions and hypocalvaria attributed to indomethacin treatment of the mother for acute polyhydramnios. History of pregnancy, postnatal clinical course, pathological findings of the kidneys, and the skulls are presented and discussed. These findings include incompletely differentiated proximal tubules in the kidneys and hypoplastic calvaria in both twins. The renal tubular lesions were more marked in the donor than in the transfused twin, probably due to the greater degree of ischemia in that twin. This seems to be in favor of a vascular etiology of the renal defects. However, the fact that similar renal lesions and hypocalvaria were also present in the transfused twin seems to indicate that indomethacin played a role in their onset. This so-called kidney-skull connection has never been reported in conjunction with indomethacin therapy.

Renin gene expression in fetal kidneys of pregnancies complicated by twin-twin transfusion syndrome

Twin-twin transfusion syndrome (TTTS) complicates one in five monochorionic pregnancies and is generally associated with high mortality and morbidity. One twin (the recipient) grows appropriately and has polyhydramnios while the other (the donor) may have a reduced growth velocity and severe oligohydramnios. The disparities in amniotic fluid volumes represent differences in fetal urine output. These differences occur secondary to hemodynamic changes, in which the vascular arrangement of placental anastomoses in TTTS leads to unidirectional flow from the donor to the recipient twin. A better understanding of the pathophysiology may contribute to improved management of this morbid condition. We studied three consecutive prospectively diagnosed stillborn twin pairs affected by early-onset TTTS. Renin gene expression was studied in sections of fetal kidneys with immunocytochemistry using a renin antiserum and with in situ hybridization using riboprobes complementary to renin mRNA, and renin-secreting cells (RCC) were counted. The overall maturation of the renal cortex was assessed by the percentage of immature glomeruli. The donor twin kidneys were smaller than those of the recipients, but the maturation of the renal cortex was not significantly different (28.2% immature glomeruli in the donor and 24.4% in the recipient kidney). The donor kidney showed increased renin gene expression with hyperplastic juxtaglomerular apparatuses (JGAs) that contained excess RCCs (median 20.02 [25th-75th centiles, 5.4, 25.1 RCCs per 100 glomeruli]). In contrast, the recipient kidney was virtually devoid of these cells (0.04 [0, 0.36] RCCs per 100 glomeruli; P < 0.05). In the donor kidney, increased renin release may, by a local action, contribute to renal vasoconstriction and oliguria. Increased renin and/or angiotensin II in the blood passing through the placental anastomoses may, by an endocrine action, suppress renin synthesis in the recipient kidney, thereby increasing renal blood flow and causing polyuria and polyhydramnios. These changes in the renal RAS could thus contribute to the pathogenesis of TTTS. The renal renin changes noted here may represent a contributory or compensating mechanism, the success of which may dictate the overall survival of the twin pregnancy and allow better understanding of the pathophysiology and perhaps therapy that may be employed in this condition.

Selective laser photocoagulation of communicating vessels in severe twin-twin transfusion syndrome in women with an anterior placenta

BACKGROUND

We describe two techniques for the laser treatment of twin-twin transfusion syndrome in women with anterior placentas.

TECHNIQUE

In the first technique, anastomoses were photocoagulated using a flexible endoscope through a single port. The second technique used a side-firing laser fiber with a rigid angled-view endoscope (two ports).

EXPERIENCE

Seventy-two women had surgery between July 1997 and December 1999, 35 (48.6%) of whom had anterior placentas. Survival was similar for fetuses with anterior (80%) and posterior (75.6%) placentas, but operating time was significantly longer for those with anterior placentas (81.1 compared with 64.4 minutes for the anterior and posterior placentas, respectively; P = .02, Student t test). At least one fetus survived in 76% (16 of 21) of women treated with flexible endoscopes and 86% (12 of 14) of those treated with the side-firing lasers. Six of 72 women (8.3%) had patent vascular anastomoses on placental examination, and five of them had anterior placentas (P = .08, Fisher exact test).

CONCLUSION

Although anterior placentas are surgically more challenging than posterior placentas, both techniques allow an effective percutaneous approach to the laser treatment of twin-twin transfusion syndrome.

[Acardius or "twin-reversed arterial prefusion" sequence. Report of four cases and review of current therapeutic possibilities]

We describe four cases of acardius (one of hemiacardius, two of holoacardius acephalus, and one of the holacardius amorphus) and present the current range of therapeutic possibilities: control of amniotic fluid by repeated amniocentesis or indomethacin therapy, administration of digoxin to the mother, selective preterm delivery of the acardiac twin by hysterotomy, interruption of the anastomoses by injection of thrombogenic coils, sclerosing agents, umbilical cord ligation, fetoscopic laser coagulation, and thermocoagulation.

Diamnionic monochorionic twin gestations: an overview

Monochorionic (MC) twins account for about 20-30% of all twins, but contribute disproportionately to mortality, intrauterine growth restriction, and preterm delivery compared with dichorionic (DC) twins. This higher mortality in MC twins is likely due to the effects of placental morphologic characteristics, which include complex vascular communications between the twins associated with twin-twin transfusion syndrome (TTTS), and the tendency for the common placenta to be shared either symmetrically or asymmetrically. In assessment of clinical outcomes for TTTS, artery to vein anastomoses in the absence of artery to artery or vein to vein, especially if present with placental asymmetry, carry the worse prognosis. Chorion status in twins forms the basis for clinical risk assessment and can be determined by 7 menstrual weeks using transvaginal sonography. The variable results reported in the literature for intertwin umbilical artery Doppler findings in MC twins may be explained by differences between sonographic and clinical criteria (including differential hemoglobin concentrations) reported by various investigators. Antenatal fetal Doppler assessment of the umbilical artery and cerebral arteries can help distinguish between TTTS and placental insufficiency in MC twins. Significant restriction of fetal growth occurs in about 25% of multiple gestations, accounting for about 17% of all growth-retarded infants. Redistribution of fetal blood (brain-sparing effect), as determined by Doppler interrogation of fetal cerebral and umbilical arteries, occurs more commonly in MC twins compared to DC twins and in growth-restricted MC twins compared to nongrowth-restricted MC twins. Overall, the prognosis is poorer for the donor twins in TTTS and there is a greater prenatal death rate for the donor (18-35%), and a higher overall survival rate for recipients following fetoscopic laser treatment. Finally, the clinical and sonographic findings suggest that the polyhydramnios/oligohydramnios sequence seen in MC twins likely represents a spectrum strongly linked to placental variables.

Congenital malformations of middle and inner ears of parabiotic twins

We describe herein the congenital malformations of the middle and inner ears in temporal bones of parabiotic, monozygotic twins. Temporal bones were removed from twin B, who had no fetal cardiac activity and was born dead at 23-4/7 weeks, and twin A, the donor or "pump" twin in intrauterine life, who died shortly after birth at 20-6/7 weeks. The temporal bones were processed routinely in celoidin, stained with hematoxylin and eosin, and examined by light microscopy. We found that twin B had Mondini's dysplasia with associated deformities of the middle ear and in general showed more developmental anomalies than twin A, and we conclude that Mondini's dysplasia with anomalies of the middle ear may occur in the parabiotic twin syndrome, and the abnormalities may be explainable as the result of vascular disturbance, which also causes other lesions in these unusual cases.

Diagnosis of twin reversed arterial perfusion sequence in the first trimester by transvaginal color Doppler ultrasound

A case of twin reversed arterial perfusion (TRAP) sequence was diagnosed at 12 weeks' gestation using transvaginal color Doppler ultrasound, which demonstrated the presence of retrograde perfusion in the umbilical artery of the abnormal twin. Ultrasound imaging showed a monochorionic-diamniotic twin pregnancy with an inappropriately grown second twin, the morphological evaluation of which revealed an abnormal cephalic pole with acrania, diffuse subcutaneous edema and the presence of cardiac activity in an abnormal heart with a single chamber.

Fetal and neonatal echocardiographic findings in twin-twin transfusion syndrome

OBJECTIVE

The study's aim was to analyze the type of cardiac involvement in fetuses or infants with twin-twin transfusion syndrome.

STUDY DESIGN

Seventeen pairs of monochorionic diamniotic twin fetuses with twin-twin transfusion syndrome underwent serial Doppler echocardiographic studies. Repeated decompressive amniocenteses were performed in all pregnancies.

RESULTS

No specific cardiac involvement was seen in donor twins in utero or after birth. All recipient twin fetuses showed variable degrees of biventricular hypertrophy and dilation with tricuspid regurgitation. These features were also evident in 45% of the recipient twin neonates. The fluid unbalance resolved with serial amniocenteses in 9 cases and in a further 2 after the death of the donor twin; in all 11 of these recipient twin fetuses there was some degree of improvement of the cardiac involvement, which became normal in all surviving recipient twin infants within 40 days to 6 months after birth.

CONCLUSION

Features of cardiac hypertrophy with signs of a prehydropic or hydropic state develop during fetal life in recipient twins in twin-twin transfusion syndrome; this impairment is reversible with the resolution of the fluid imbalance or after delivery.

Alterations in myelin formation in fetal brains of twins

Insufficient nutrition is known to lead to disturbances in postnatal myelin formation. This study aims to demonstrate that early myelination is altered in human twin pregnancies. Five brains of twins with a symmetric blood supply and three brains of twins with chronic fetal-fetal transfusion syndrome (one hypervolemic acceptor and two hypoxemic donors) were investigated and compared with six brains of singletons. The globus pallidus, where myelination normally starts within the prosencephalon, was studied immunohistochemically using antibodies against myelin basic protein (MBP) and with the aid of electron microscopy. In twins and donors, MBP-immunostained somata of myelin-forming oligodendrocytes were packed densely within the globus pallidus, whereas in singletons and acceptors an intense fibrous immunoreactivity was observed. Electron micrographs revealed noncompacted myelin in twins, whereas in singletons the multilaminar structure of compact myelin was observed. The results demonstrate a distinct qualitative alteration in myelination because of nutritional insufficiency during pregnancy. The lack of MBP-positive fibers (i.e., compact myelin sheaths) may be correlated to impaired maturation of oligodendroglia. The alterations described here may reflect a delayed incorporation of MBP into the processes so that the formation of compact myelin is retarded.

Vascular anatomy of monochorionic placenta in relation to discordant growth and amniotic fluid volume

The objective of this study was to determine the chorionic plate vascular anatomy of the monochorionic (MC) placenta in relation to the discordance in fetal growth with or without disparity in amniotic fluid volume. In 58 MC placentae, anastomoses were delineated by dye-contrast injection under optimal physiological conditions. Thirty-two pregnancies were complicated by twin-twin transfusion syndrome (TTTS) (n = 32), of which 16 placentae were from severe disease. Ten pregnancies with fetal growth discordance of >20% and with a normal amniotic fluid index (AFI) were also studied. Sixteen uncomplicated MC pregnancies were used as controls. Severe TTTS placentae (median, m 1; range, r 0 to 2) had significantly fewer anastomoses than those from mild disease (m 2; r 1 to 4; P < 0.01), discordant growth (m 3; r 2 to 6; P < 0.001) and controls (m 5; r 2 to 8; P < 0.001). Placentae from severe TTTS had a single unidirectional deep arteriovenous anastomosis, while milder cases, in addition, had a < or = 1 mm bidirectional superficial arterioarterial (n = 9) or venovenous (n = 6) -type shunts. Multiple arteriovenous anastomoses with a paucity of superficial anastomoses were detected in discordant growth placenta. In contrast, control placentae had multiple shunts which were symmetrical in number, type and size both overall and per placenta. The subchorionic distance in severe TTTS and discordant growth placenta were comparable (m 3.5 cm; r 1.6 to 5.8 cm versus m 3.6 cm; r 2.5 to 5.7 cm), but were greater than the mild disease (m 2.5 cm; r 1.2 to 3.8 cm; P < 0.01) and control groups (m 1 cm; r 0.5 to 2.4 cm; P < 0.001). The perinatal mortality in severe TTTS (57%) was higher than that in the mild TTTS (17%) and growth discordant groups (15%). The paucity of superficial anastomoses with presence of solitary or multiple arteriovenous anastomoses is likely to be associated with severe TTTS and fetal growth discordance of >20% respectively. In contrast, in mild TTTS additional superficial arterioarterial or venovenous channels are present along with single deep arteriovenous anastomoses.

[Prenatal diagnosis and therapy of feto-fetal transfusion syndrome]

Twin-twin transfusion syndrome (TTTS) is a serious complication of monochorionic twin pregnancies. It is the result of an unbalanced transfusion of blood across placental vascular anastomoses. TTTS appears predominantly in the second trimester of pregnancy characterized by discordance of growth as well as polyhydramnios in the recipient and oligo-/anhydramnios in the donor. Prenatal diagnosis is possible by non-invasive and invasive methods. The prognosis of the untreated TTTS is very poor. Serial amniocenteses and laser therapy are used resulting in survival rates of about 60%. Intrauterine death of one twin is associated with a high risk of morbidity in the surviving twin. Monochroionic twins have to be identified in early pregnancy. Close surveillance is necessary to diagnose TTTS at an early stage of the disease.

Chorionic plate vascular anatomy determines the efficacy of amnioreduction therapy for twin-twin transfusion syndrome

The objective of the study was to determine whether vascular anatomy of monochorial placenta influences the therapeutic efficacy of serial amnioreduction in chronic mid-trimester twin-twin transfusion syndrome (TTTS). Twenty-six consecutive monochorial pregnancies complicated by TTTS and treated by serial amnioreduction were studied. The placental anastomoses were delineated postnatally by perfusion studies. Amniotic fluid index, amniotic fluid pressure, number of amnioreductions, interval between amnioreduction, and neonatal outcome were correlated with the presence or absence of superficial anastomotic channels and type of cord insertion. Placentae were divided into two groups according to the presence (n = 9) and absence (n = 14) of superficial anastomosis. Gestational age at diagnosis, delivery, percentage discordance in estimated birth weight were comparable in the two groups. The amniotic fluid index, liquor volume removed, and amniotic pressure at first amnioreduction were also comparable between groups. In the group without superficial arterio-arterial/veno-venous (AA/VV) anastomoses, amnioreduction was required more often (P < 0.05). Perinatal mortality in terms of intrauterine deaths (IUD) and neonatal death was more common in the group without AA/VV anastomotic channels (P < 0.05). There was no difference in incidence of velamentous/marginal cord insertion between the two groups. TTTS lacking superficial AA or VV anastomosis are more likely to require frequent amnioreduction and are associated with increased perinatal mortality and morbidity, whereas the presence of such shunts was associated with increased therapeutic efficacy of amnioreduction and a more favourable prognosis.

Placental anatomy, fetal demise and therapeutic intervention in monochorionic twins and the transfusion syndrome: new hypotheses

OBJECTIVE

Monochorionic twins with circulatory sharing have an incompletely understood response to acute hemodynamic events. We relate placental vascular anatomy with, first, the response to (a) acute fetal demise and (b) laser interrupted placental anastomoses and, second, the efficacy of current and possibly future therapeutic interventions in twin-twin transfusion syndrome.

DESIGN

Hemodynamic response to acute fetal demise and laser interrupted anastomoses is analysed using the model previously developed for monochorionic twins. Efficacy of therapeutic interventions in twin-twin transfusion syndrome is analysed by combining the estimated incidence of placental anastomotic patterns with three previously proposed pathophysiologic mechanisms.

RESULTS

Fetal demise may cause sequelae for the co-twin in all anastomotic patterns except unidirectional arteriovenous and single venovenous anastomoses which are predicted to be hemodynamically harmless. In twin-twin transfusion syndrome, laser interruption of all anastomoses mitigates further transfusion. This is of benefit for the twins in equally but not in unequally shared placentas. Analysis predicts that approximately 75% fetal survival could be achieved interrupting only arteriovenous anastomoses. Amniocentesis may only prolong pregnancies that lack progressively increasing discordance, assuming that placental anastomoses remain patent following polyhydramnios. This proposed mechanism of action predicts current therapeutic efficacy accurately and could explain the significantly higher reported serious morbidity compared with laser (15/81 = 19+/-5% versus 4/146=3%, P=0.00004). However, if therapeutic interventions could match the syndrome's individual placental anatomy, the analysis suggests approximately 10-15% laser related mortality (premature rupture of membranes) and <3% severe morbidity could possibly become achievable goals.

CONCLUSION

Our predictions allow clinical testing. This information may contribute to an improved management of monochorionic twins.

[Monozygotic multiple pregnancies with acardiac anomalies]

The acardiac fetus is a rare anomaly of about 1 percent of monozygotic pregnancies, occurring in approximately 1 in 35,000 pregnancies. The special hemodynamic circumstances of the normal heart having to pump an excessive amount of blood for a long period of time will influence the chance of survival of this fetus. In two case-report with many figures pathologic-anatomical problems and prospective management to improve the outcome of monozygotic multiple pregnancies complicated by acardiac malformation were presented. The pathogenesis of metabolic dysbalance in these pregnancies was discussed.

Placental pathophysiology of the twin oligohydramnios-polyhydramnios sequence and the twin-twin transfusion syndrome

Currently accepted sonographic criteria for antenatal diagnosis of twin-twin transfusion (TTT) syndrome include a monochorionic placenta with same-sex twins, marked growth discordance, and oligohydramnios of the growth-retarded twin with coexistent polyhydramnios of the larger twin. Our previous report of nine women fulfilling these criteria, examined using sequential funipuncture of both fetuses, demonstrated inter-twin blood transfusion in only four cases (44 per cent). It was proposed that traditional sonographic criteria actually describe a heterogeneous group of disorders more appropriately described as the twin oligohydramnios-polydramnios sequence (TOPS). True TTT is a subset of this population, the antenatal diagnosis of which requires specific demonstration of transfusion from one fetus (donor) to the other (recipient). In this report, antenatal placental evaluation has been correlated using duplex pulsed-wave Doppler analysis of arterial blood flow velocity with postpartum gross and histopathologic evaluation of the placenta, with special attention to microvasculature. There was a higher incidence of resistance to blood flow, abnormal umbilical cord insertion, and diminished placental microvasculature associated with oligohydramnic growth-retarded (donor) twins when compared with polyhydramnic (recipient) twins. Based on these observations, it is proposed that TTT and TOPS represent asymmetric placental insufficiency resulting from aberrant placentation.

Velamentous cord insertion in monochorionic twin gestation. An added risk factor

OBJECTIVE

To study the effects of umbilical cord insertion combinations on outcomes in monochorionic (MC) twin placentas.

STUDY DESIGN

Sixty consecutive MC placentas were analyzed by cord insertion patterns with regard to growth discordance, placental parenchymal sharing, types and patterns of intertwin vascular anastomoses, perinatal mortality and frequency of fetofetal transfusion. Cord insertions were classified as central/eccentric (CEN) or velamentous/marginal (VEL).

RESULTS

Forty-five percent of the twins had VEL insertions. The CEN/VEL combination was found in 53% of pairs. The CEN/VEL group had the highest rates of growth discordance > 20%, unequal placental parenchymal sharing, uncompensated anastomoses and perinatal demise.

CONCLUSION

VEL cord insertion and the CEN/VEL combination are indicators of high-risk subgroups within MC twins. VEL cord insertions can be diagnosed by ultrasound, identifying these high-risk groups.

The aetiology and management of twin-twin transfusion syndrome

Twin-to-twin transfusion syndrome presents in the mid-trimester with gross discordance in amniotic fluid volume, and complicates 10-15 per cent of monochorionic twins. Recent studies suggest a primary vascular basis in which a paucity of the bidirectional superficial anastomoses normally found in monochorionic twins is unable to compensate for haemodynamic imbalance resulting from unidirectional transfusion along deeper arterio-venous anastomoses. It is associated with high rates of perinatal mortality from ruptured membranes, hydrops and growth restriction, and a significant morbidity from cardiac and neurological sequelae in particular. Serial aggressive amnioreduction is the current treatment of choice, with survival in around two thirds of cases. In the remaining third, with features suggesting a poor outcome, selective fetocide may have a role. Current attempts at vascular ablative therapies have been associated with inferior survival rates, but the long term therapeutic goal remains the identification and ablation of the shared chorionic vasculature.

The umbilical pump: a contributor to twin-twin transfusion

BACKGROUND

Umbilical vascular coiling may function as a rudimentary pump that facilitates venous return from the placenta.

CASES

Three consecutive twin gestations with twin-twin transfusion syndrome were evaluated prospectively at delivery. The birth weights and umbilical coiling indices of donor and recipient twins were compared. The umbilical coiling index was determined by dividing the number of complete vascular coils in a given umbilical cord by the cord's length in centimeters. In each case, the recipient twin was larger at birth and had an umbilical coiling index value that was at least twice that of the corresponding donor twin.

CONCLUSION

Differential umbilical vascular coiling densities among monochorionic twins may play a role in the pathogenesis of twin-twin transfusion syndrome.

Twin transfusion syndrome: reassessment of ultrasound diagnosis

OBJECTIVE

To assess the antenatal ultrasonic diagnosis of the twin transfusion syndrome, an enigmatic disorder that results in an imbalance in the blood flow between monochorionic twins.

STUDY DESIGN

Retrospective review of 16 cases of twin transfusion syndrome confirmed by placental pathology and neonatal data.

RESULTS

A disparity in antenatal fetal weights, size difference between the two amniotic sacs and a single placenta were present in 81% (13/16) of confirmed cases. The finding of two separate umbilical cords with a disparity in the size or number of vessels was rare. Evidence of hydrops in either fetus or findings of congestive cardiac failure in the recipient twin were uncommon.

CONCLUSION

Our data strongly suggest that the twin transfusion syndrome can be diagnosed in a significant number (81%) of cases. The syndrome is variable, and it is rare to observe all the diagnostic criteria in one case.

Lenticulostriate vasculopathy in twin-to-twin transfusion syndrome: sonographic and CT findings

Lenticulostriate vasculopathy can be seen in an increasing number of clinical conditions, among which congenital infections and chromosomal abnormalities are best known. Two further patients with this ultrasound finding are reported, who were both recipients in the twin-to-twin transfusion syndrome.

Twin transfusion: pathological studies of the monochorionic placenta in liveborn twins and of the perinatal autopsy in monochorionic twin pairs

Vascular injections of 21 monochorionic placentas from liveborn twins were scored for chorionic surface vessel anastomoses and for venous return areas. The results were correlated with neonatal birth weight and first hematocrit. Weight and hematocrit differences did not correlate with each other or with placental anastomoses. There was a relationship between weight and placental area to the individual twin. In some cases, weight differences between monochorionic twins may be the result of placental differences rather than chronic transfusion. Seventeen perinatal autopsies of monochorionic twin pairs were reviewed for plethora/pallor and for organ and body weights. Cardiac hypertrophy was present in three autopsies. Cardiac hypertrophy may be a measure of chronic twin transfusion in the recipient. The lighter twin was as likely to be plethoric as the heavier. Plethora postmortem is a poor measure of chronic transfusion because of confounding factors, particularly acute twin transfusion. As a result of these studies, placental anatomy is speculated to be complexly rather than directly related to clinical outcome.

Angioarchitecture of monochorionic placentas in relation to the twin-twin transfusion syndrome

OBJECTIVE

Twin-twin transfusion syndrome in the midtrimester is associated with a perinatal mortality rate exceeding 80%. Although attributed to intertwin transfusion along vascular anastomoses, these occur in all monochorial placentas, not just the 10% with twin-twin transfusion syndrome. We compared fetoplacental angioarchitecture in monochorionic twin placentas with and without twin-twin transfusion syndrome.

STUDY DESIGN

The fetoplacental circulations of both twins in 20 monochorial placentas were perfused immediately after delivery under optimal physiologic conditions and anastomoses delineated by dye-contrast injection. Ten were from pregnancies with evidence of midtrimester twin-twin transfusion syndrome and 10 were from pregnancies without twin-twin transfusion syndrome.

RESULTS

Placentas from pregnancies with twin-twin transfusion syndrome had significantly fewer anastomoses than did those without twin-twin transfusion syndrome, both overall (median one versus six, respectively; p < 0.001) and for each of the different types (arterioarterial, venovenous, and arteriovenous, p < 0.001). Whereas multiple anastomoses were present in all controls, only one twin-twin transfusion syndrome placenta had more than a single communication. Anastomoses in the twin-twin transfusion syndrome group were more likely to be of the deep than the superficial type (80% vs 36% in controls, p < 0.01).

CONCLUSIONS

Placental vascular anastomoses in monochorial pregnancies complicated by twin-twin transfusion syndrome are both fewer in number and of a different type than those without twin-twin transfusion syndrome. These differences seem implicated in the underlying pathophysiologic features of twin-twin transfusion syndrome and are of relevance to the development of newer therapies such as placental laser surgery.

Clinical and echographic features of in utero cardiac dysfunction in the recipient twin in twin-twin transfusion syndrome

OBJECTIVE

Fetal twin-twin transfusion syndrome (TTTS) presenting in the second trimester has been associated with almost no perinatal survival until recently, when serial drainage of amniotic fluid has improved the prognosis to 70%-80%. Most recipient twins now survive but develop cardiac dysfunction. The study was undertaken to evaluate the abnormal echocardiographic features and clinical complications of cardiac disease in the recipient twin of TTTS.

DESIGN

Antenatal and postnatal echocardiographic and clinical observational study.

SETTING

Antenatal studies in a tertiary referral centre. Postnatal management and follow up were performed by the same paediatric cardiologist, either at the obstetric hospital or at the regional referral centre.

PATIENTS

Twin pregnancies complicated by TTTS with severe polyhydramnios diagnosed earlier than 25 weeks that proceeded until viability (n = 5).

INTERVENTION

Serial fetal echocardiography with colour Doppler. Postnatal echocardiography in the first week and between two and seven months. Serial amnioreduction was performed in all pregnancies. Digoxin treatment, pericardiocentesis, paracentesis, or laser ablation of placental anastomoses was undertaken when there was hydrops.

RESULTS

Increased cardiothoracic ratio and tricuspid regurgitation were seen in all recipient twins. High pulmonary artery velocities developed in three. One recipient twin died a week after delivery of endocardial fibroelastosis and infundibular pulmonary stenosis. Two other had balloon dilatation for pulmonary stenosis, one shortly after birth and one at four months. A further twin has apical thickening of the right ventricle at six months. The remaining recipient twin had normal echocardiographic findings at follow up.

CONCLUSION

This report characterises for the first time a cardiac disease acquired in utero in the recipient twin in pregnancies complicated by TTTS. Clinical manifestations in utero range from mild to critical pulmonary stenosis or lethal cardiomyopathy. Although perinatal prognosis seems to be related to the severity of dysfunction when first diagnosed in utero, follow up in infancy is recommended in view of the possibility of progressive pulmonary stenosis.