Twin-twin transfusion syndrome
2012; Elsevier BV; Volume: 208; Issue: 1 Linguagem: Inglês
10.1016/j.ajog.2012.10.880
ISSN1097-6868
Autores Tópico(s)Ectopic Pregnancy Diagnosis and Management
ResumoObjectiveWe sought to review the natural history, pathophysiology, diagnosis, and treatment options for twin-twin transfusion syndrome (TTTS).MethodsA systematic review was performed using MEDLINE database, PubMed, EMBASE, and Cochrane Library. The search was restricted to English-language articles published from 1966 through July 2012. Priority was given to articles reporting original research, in particular randomized controlled trials, although review articles and commentaries also were consulted. Abstracts of research presented at symposia and scientific conferences were not considered adequate for inclusion in this document. Evidence reports and guidelines published by organizations or institutions such as the National Institutes of Health, Agency for Health Research and Quality, American College of Obstetricians and Gynecologists, and Society for Maternal-Fetal Medicine were also reviewed, and additional studies were located by reviewing bibliographies of identified articles. Consistent with US Preventive Task Force guidelines, references were evaluated for quality based on the highest level of evidence, and recommendations were graded accordingly.Results and RecommendationsTTTS is a serious condition that can complicate 8-10% of twin pregnancies with monochorionic diamniotic (MCDA) placentation. The diagnosis of TTTS requires 2 criteria: (1) the presence of a MCDA pregnancy; and (2) the presence of oligohydramnios (defined as a maximal vertical pocket of 8 cm) in the other sac. The Quintero staging system appears to be a useful tool for describing the severity of TTTS in a standardized fashion. Serial sonographic evaluation should be considered for all twins with MCDA placentation, usually beginning at around 16 weeks and continuing about every 2 weeks until delivery. Screening for congenital heart disease is warranted in all monochorionic twins, in particular those complicated by TTTS. Extensive counseling should be provided to patients with pregnancies complicated by TTTS including natural history of the disease, as well as management options and their risks and benefits. The natural history of stage I TTTS is that more than three-fourths of cases remain stable or regress without invasive intervention, with perinatal survival of about 86%. Therefore, many patients with stage I TTTS may often be managed expectantly. The natural history of advanced (eg, stage ≥III) TTTS is bleak, with a reported perinatal loss rate of 70-100%, particularly when it presents <26 weeks. Fetoscopic laser photocoagulation of placental anastomoses is considered by most experts to be the best available approach for stages II, III, and IV TTTS in continuing pregnancies at <26 weeks, but the metaanalysis data show no significant survival benefit, and the long-term neurologic outcomes in the Eurofetus trial were not different than in nonlaser-treated controls. Even laser-treated TTTS is associated with a perinatal mortality rate of 30-50%, and a 5-20% chance of long-term neurologic handicap. Steroids for fetal maturation should be considered at 24 0/7 to 33 6/7 weeks, particularly in pregnancies complicated by stage ≥III TTTS, and those undergoing invasive interventions. We sought to review the natural history, pathophysiology, diagnosis, and treatment options for twin-twin transfusion syndrome (TTTS). A systematic review was performed using MEDLINE database, PubMed, EMBASE, and Cochrane Library. The search was restricted to English-language articles published from 1966 through July 2012. Priority was given to articles reporting original research, in particular randomized controlled trials, although review articles and commentaries also were consulted. Abstracts of research presented at symposia and scientific conferences were not considered adequate for inclusion in this document. Evidence reports and guidelines published by organizations or institutions such as the National Institutes of Health, Agency for Health Research and Quality, American College of Obstetricians and Gynecologists, and Society for Maternal-Fetal Medicine were also reviewed, and additional studies were located by reviewing bibliographies of identified articles. Consistent with US Preventive Task Force guidelines, references were evaluated for quality based on the highest level of evidence, and recommendations were graded accordingly. TTTS is a serious condition that can complicate 8-10% of twin pregnancies with monochorionic diamniotic (MCDA) placentation. The diagnosis of TTTS requires 2 criteria: (1) the presence of a MCDA pregnancy; and (2) the presence of oligohydramnios (defined as a maximal vertical pocket of 8 cm) in the other sac. The Quintero staging system appears to be a useful tool for describing the severity of TTTS in a standardized fashion. Serial sonographic evaluation should be considered for all twins with MCDA placentation, usually beginning at around 16 weeks and continuing about every 2 weeks until delivery. Screening for congenital heart disease is warranted in all monochorionic twins, in particular those complicated by TTTS. Extensive counseling should be provided to patients with pregnancies complicated by TTTS including natural history of the disease, as well as management options and their risks and benefits. The natural history of stage I TTTS is that more than three-fourths of cases remain stable or regress without invasive intervention, with perinatal survival of about 86%. Therefore, many patients with stage I TTTS may often be managed expectantly. The natural history of advanced (eg, stage ≥III) TTTS is bleak, with a reported perinatal loss rate of 70-100%, particularly when it presents <26 weeks. Fetoscopic laser photocoagulation of placental anastomoses is considered by most experts to be the best available approach for stages II, III, and IV TTTS in continuing pregnancies at <26 weeks, but the metaanalysis data show no significant survival benefit, and the long-term neurologic outcomes in the Eurofetus trial were not different than in nonlaser-treated controls. Even laser-treated TTTS is associated with a perinatal mortality rate of 30-50%, and a 5-20% chance of long-term neurologic handicap. Steroids for fetal maturation should be considered at 24 0/7 to 33 6/7 weeks, particularly in pregnancies complicated by stage ≥III TTTS, and those undergoing invasive interventions. Twin-twin transfusion syndrome (TTTS) is diagnosed prenatally by ultrasound. The diagnosis requires 2 criteria: (1) the presence of a monochorionic diamniotic (MCDA) pregnancy; and (2) the presence of oligohydramnios (defined as a maximal vertical pocket [MVP] of 8 cm) in the other sac (Figure 1).1Simpson L.L. Twin-twin transfusion syndrome.in: Copel J.A. Obstetric imaging. 1st ed. Elsevier, Philadelphia2012Google Scholar MVP of 2 cm and 8 cm represent the 5th and 95th percentiles for amniotic fluid measurements, respectively, and the presence of both is used to define stage I TTTS.2Quintero R.A. Morales W.J. Allen M.H. Bornick P.W. Johnson P.K. Kruger M. Staging of twin-twin transfusion syndrome.J Perinatol. 1999; 19 (Level II-3): 550-555Crossref PubMed Scopus (1143) Google Scholar If there is a subjective difference in amniotic fluid in the 2 sacs that fails to meet these criteria, progression to TTTS occurs in 20%) and intrauterine growth restriction (IUGR) (estimated fetal weight 1.5 multiples of median in the donor and MCA PSV <1.0 multiples of median in the recipient, in the absence of oligohydramnios-polyhydramnios.6Slaghekke F. Kist W.J. Oepkes D. et al.Twin anemia-polycythemia sequence: diagnostic criteria, classification, perinatal management and outcome.Fetal Diagn Ther. 2010; 27 (Level II-3): 181-190Crossref PubMed Scopus (288) Google Scholar Further studies are required to determine the natural history and possible management of TAPS. TTTS can occur in a MCDA twin pair in triplet or higher-order pregnancies. The most commonly used TTTS staging system was developed by Quintero et al2Quintero R.A. Morales W.J. Allen M.H. Bornick P.W. Johnson P.K. Kruger M. Staging of twin-twin transfusion syndrome.J Perinatol. 1999; 19 (Level II-3): 550-555Crossref PubMed Scopus (1143) Google Scholar in 1999, and is based on sonographic findings. The TTTS Quintero staging system includes 5 stages, ranging from mild disease with isolated discordant amniotic fluid volume to severe disease with demise of one or both twins (Table 1 and FIGURE 2, FIGURE 3). This system has some prognostic significance and provides a method to compare outcome data using different therapeutic interventions.2Quintero R.A. Morales W.J. Allen M.H. Bornick P.W. Johnson P.K. Kruger M. Staging of twin-twin transfusion syndrome.J Perinatol. 1999; 19 (Level II-3): 550-555Crossref PubMed Scopus (1143) Google Scholar Although the stages do not correlate perfectly with perinatal survival,7Taylor M.J. Govender L. Jolly M. Wee L. Fisk N.M. Validation of the Quintero staging system for twin-twin transfusion syndrome.Obstet Gynecol. 2002; 100 (Level II-2): 1257-1265Crossref PubMed Scopus (111) Google Scholar it is relatively straightforward to apply, may improve communication between patients and providers, and identifies the subset of cases most likely to benefit from treatment.8Stamilio D.M. Fraser W.D. Moore T.R. Twin-twin transfusion syndrome: an ethics-based and evidence-based argument for clinical research.Am J Obstet Gynecol. 2010; 203 (Level III): 3-16Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar, 9Rossi A.C. D'Addario V. The efficacy of Quintero staging system to assess severity of twin-twin transfusion syndrome treated with laser therapy: a systematic review with meta-analysis.Am J Perinatol. 2009; 26 (Level II-1): 537-544Crossref PubMed Scopus (42) Google ScholarTABLE 1Staging of twin-twin transfusion syndrome2Quintero R.A. Morales W.J. Allen M.H. Bornick P.W. Johnson P.K. Kruger M. Staging of twin-twin transfusion syndrome.J Perinatol. 1999; 19 (Level II-3): 550-555Crossref PubMed Scopus (1143) Google ScholarStageUltrasound parameterCategorical criteriaIMVP of amniotic fluidMVP 8 cm in recipient sacIIFetal bladderNonvisualization of fetal bladder in donor twin over 60 min of observation (Figure 2)IIIUmbilical artery, ductus venosus, and umbilical vein Doppler waveformsAbsent or reversed umbilical artery diastolic flow, reversed ductus venosus a-wave flow, pulsatile umbilical vein flow (Figure 3)IVFetal hydropsHydrops in one or both twinsVAbsent fetal cardiac activityFetal demise in one or both twinsMVP, maximal vertical pocket.SMFM. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013. Open table in a new tab FIGURE 3Stage III twin-twin transfusion syndromeReproduced with permission from Simpson.1Simpson L.L. Twin-twin transfusion syndrome.in: Copel J.A. Obstetric imaging. 1st ed. Elsevier, Philadelphia2012Google ScholarShow full captionAbsent end-diastolic flow (arrows) in umbilical artery of donor twin.SMFM. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013.View Large Image Figure ViewerDownload Hi-res image Download (PPT) MVP, maximal vertical pocket. SMFM. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013. Absent end-diastolic flow (arrows) in umbilical artery of donor twin. SMFM. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013. Since the development of the Quintero staging system, much has been learned about the changes in fetal cardiovascular physiology that accompany disease progression (discussed below). Myocardial performance abnormalities have been described, particularly in recipient twins, including those with only stage I or II TTTS.10Habli M. Michelfelder E. Cnota J. et al.Prevalence and progression of recipient-twin cardiomyopathy in early-stage twin-twin transfusion syndrome.Ultrasound Obstet Gynecol. 2012; 39 (Level II-2): 63-68Crossref PubMed Scopus (50) Google Scholar Several groups of investigators have attempted to use assessment of fetal cardiac function to either modify the Quintero TTTS stage11Michelfelder E. Gottliebson W. Border W. et al.Early manifestations and spectrum of recipient twin cardiomyopathy in twin-twin transfusion syndrome: relation to Quintero stage.Ultrasound Obstet Gynecol. 2007; 30 (Level II-2): 965-971Crossref PubMed Scopus (138) Google Scholar or develop a new scoring system.12Rychik J. Tian Z. Bebbington M. et al.The twin-twin transfusion syndrome: spectrum of cardiovascular abnormality and development of a cardiovascular score to assess severity of disease.Am J Obstet Gynecol. 2007; 197 (Level II-2): 392.e1-392.e8Abstract Full Text Full Text PDF PubMed Scopus (220) Google Scholar While this approach has some benefits, the models have not yet been prospectively validated. As a result, a recent expert panel concluded that there were insufficient data to recommend modifying the Quintero staging system or adopting a new system.8Stamilio D.M. Fraser W.D. Moore T.R. Twin-twin transfusion syndrome: an ethics-based and evidence-based argument for clinical research.Am J Obstet Gynecol. 2010; 203 (Level III): 3-16Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar Thus, despite debate over the merits of the Quintero system, at this time it appears to be a useful tool for the diagnosis of TTTS, as well as for describing its severity, in a standardized fashion. Approximately one-third of twins are monozygotic (MZ), and three-fourths of MZ twins are MCDA. In general, only twin gestations with MCDA placentation are at significant risk for TTTS, which complicates about 8-10% of MCDA pregnancies.13Lewi L. Jani J. Blickstein I. et al.The outcome of monochorionic diamniotic twin gestations in the era of invasive fetal therapy: a prospective cohort study.Am J Obstet Gynecol. 2008; 199 (Level II-1): 514.e1-514.e8Abstract Full Text Full Text PDF PubMed Scopus (431) Google Scholar, 14Acosta-Rojas R. Becker J. Munoz-Abellana B. et al.Twin chorionicity and the risk of adverse perinatal outcome.Int J Gynaecol Obstet. 2007; 96 (Level II-2): 98-102Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar TTTS is very uncommon in MZ twins with dichorionic or monoamniotic placentation.15Hack K.E. van Gemert M.J. Lopriore E. et al.Placental characteristics of monoamniotic twin pregnancies in relation to perinatal outcome.Placenta. 2009; 30 (Level II-2): 62-65Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar Although most twins conceived with in vitro fertilization (IVF) are dichorionic, it is important to remember that there is a 2- to 12-fold increase in MZ twinning in embryos conceived with IVF, and TTTS can therefore occur for IVF MCDA pregnancies.16Blickstein I. Estimation of iatrogenic monozygotic twinning rate following assisted reproduction: pitfalls and caveats.Am J Obstet Gynecol. 2005; 192 (Level III): 365-386Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 17Aston K.I. Peterson C.M. Carrell D.T. Monozygotic twinning associated with assisted reproductive technologies: a review.Reproduction. 2008; 172 (Level III): 377-386Crossref Scopus (172) Google Scholar In current practice, the prevalence of TTTS is approximately 1-3 per 10,000 births.18Blickstein I. Monochorionicity in perspective.Ultrasound Obstet Gynecol. 2006; 27 (Level III): 235-238Crossref PubMed Scopus (28) Google Scholar The presentation of TTTS is highly variable. Because pregnancies with TTTS often receive care at referral centers, data about the stage of TTTS at initial presentation (ie, to nonreferral centers) are lacking in the literature. Fetal therapy centers report that about 11-15% of their cases at referral were Quintero stage I (probably underestimated as some referral centers did not report stage I TTTS cases), 20-40% were stage II, 38-60% were stage III, 6-7% were stage IV, and 2% were stage V.5Gandhi M. Papanna R. Teach M. Johnson A. Moise K.J.J. Suspected twin-twin transfusion syndrome: how often is the diagnosis correct and referral timely?.J Ultrasound Med. 2012; 31 (Level II-2): 941-945PubMed Google Scholar, 9Rossi A.C. D'Addario V. The efficacy of Quintero staging system to assess severity of twin-twin transfusion syndrome treated with laser therapy: a systematic review with meta-analysis.Am J Perinatol. 2009; 26 (Level II-1): 537-544Crossref PubMed Scopus (42) Google Scholar Although TTTS may develop at any time in gestation, the majority of cases are diagnosed in the second trimester. Stage I may progress to a nonvisualized fetal bladder in the donor (stage II) (Figure 2), and absent or reversed end-diastolic flow in the umbilical artery of donor or recipient twins may subsequently develop (stage III) (Figure 3), followed by hydrops (stage IV). However, TTTS often does not progress in a predictable manner. Natural history data by stage are limited, especially for stages II-V, as staging was initially proposed in 1999.2Quintero R.A. Morales W.J. Allen M.H. Bornick P.W. Johnson P.K. Kruger M. Staging of twin-twin transfusion syndrome.J Perinatol. 1999; 19 (Level II-3): 550-555Crossref PubMed Scopus (1143) Google Scholar This is because most natural history data were published before 1999, and therefore was not stratified by stage (Table 2).19Bebbington M.W. Tiblad E. Huesler-Charles M. Wilson R.D. Mann S.E. Johnson M.P. Outcomes in a cohort of patients with stage I twin-to-twin transfusion syndrome.Ultrasound Obstet Gynecol. 2010; 36 (Level II-2): 48-51Crossref PubMed Scopus (45) Google Scholar, 20Rossi C. D'Addario V. Survival outcomes of twin-twin transfusion syndrome in stage I: a systematic review of the literature.Am J Perinatol. 2012, July 26; ([epub ahead of print]. Level II-1)PubMed Google Scholar, 21Meriki N. Smoleniec J. Challis D. Welsh A.W. Immediate outcome of twin-twin transfusion syndrome following selective laser photocoagulation of communicating vessels at the NSW fetal therapy center.Aust N Z J Obstet Gynaecol. 2010; 50 (Level II-2): 112-119Crossref PubMed Scopus (30) Google Scholar Over three fourths of stage I TTTS cases remain stable or regress without invasive interventions (Table 2).19Bebbington M.W. Tiblad E. Huesler-Charles M. Wilson R.D. Mann S.E. Johnson M.P. Outcomes in a cohort of patients with stage I twin-to-twin transfusion syndrome.Ultrasound Obstet Gynecol. 2010; 36 (Level II-2): 48-51Crossref PubMed Scopus (45) Google Scholar, 20Rossi C. D'Addario V. Survival outcomes of twin-twin transfusion syndrome in stage I: a systematic review of the literature.Am J Perinatol. 2012, July 26; ([epub ahead of print]. Level II-1)PubMed Google Scholar, 21Meriki N. Smoleniec J. Challis D. Welsh A.W. Immediate outcome of twin-twin transfusion syndrome following selective laser photocoagulation of communicating vessels at the NSW fetal therapy center.Aust N Z J Obstet Gynaecol. 2010; 50 (Level II-2): 112-119Crossref PubMed Scopus (30) Google Scholar The natural history of advanced (eg, stage ≥III) TTTS is bleak, with a reported perinatal loss rate of 70-100%, particularly when it presents <26 weeks.22Berghella V. Kaufmann M. Natural history of twin-twin transfusion syndrome.J Reprod Med. 2001; 46 (Level II-2): 480-484PubMed Google Scholar, 23Gul A. Aslan H. Polat I. et al.Natural history of 11 cases of twin-twin transfusion syndrome without intervention.Twin Res. 2003; 6 (Level II-2): 263-266PubMed Google Scholar It is estimated that TTTS accounts for up to 17% of the total perinatal mortality in twins, and for about half of all perinatal deaths in MCDA twins.13Lewi L. Jani J. Blickstein I. et al.The outcome of monochorionic diamniotic twin gestations in the era of invasive fetal therapy: a prospective cohort study.Am J Obstet Gynecol. 2008; 199 (Level II-1): 514.e1-514.e8Abstract Full Text Full Text PDF PubMed Scopus (431) Google Scholar, 24Steinberg L.H. Hurley V.A. Desmedt E. Beischer N.A. Acute polyhydramnios in twin pregnancies.Aust N Z J Obstet Gynaecol. 1990; 30 (Level II-3): 196-200Crossref PubMed Scopus (41) Google Scholar Without treatment, the loss of at least 1 fetus is common, with demise of the remaining twin occurring in about 10% of cases of twin demise, and neurologic handicap affecting 10-30% of cotwin remaining survivors.25Urig M.A. Clewell W.H. Elliott J.P. Twin-twin transfusion syndrome.Am J Obstet Gynecol. 1990; 163 (Level II-2): 1522-1526Abstract Full Text PDF PubMed Scopus (161) Google Scholar, 26van Heteren C.F. Nijhuis J.G. Semmekrot B.A. Mulders L.G. van den Berg P.P. Risk for surviving twin after fetal death of co-twin in twin-twin transfusion syndrome.Obstet Gynecol. 1998; 92 (Level II-2): 215-219Crossref PubMed Scopus (95) Google Scholar, 27Ong S.S. Zamora J. Khan K.S. Kilby M.D. Prognosis for the co-twin following single-twin death: a systematic review.BJOG. 2006; 113 (Level II-1): 992-998Crossref PubMed Scopus (220) Google Scholar Overall, single twin survival rates in TTTS vary widely between 15-70%, depending on the gestational age at diagnosis and severity of disease.22Berghella V. Kaufmann M. Natural history of twin-twin transfusion syndrome.J Reprod Med. 2001; 46 (Level II-2): 480-484PubMed Google Scholar, 26van Heteren C.F. Nijhuis J.G. Semmekrot B.A. Mulders L.G. van den Berg P.P. Risk for surviving twin after fetal death of co-twin in twin-twin transfusion syndrome.Obstet Gynecol. 1998; 92 (Level II-2): 215-219Crossref PubMed Scopus (95) Google Scholar The lack of a predictable natural history, and therefore the uncertain prognosis for TTTS, pose a significant challenge to the clinician caring for MCDA twins.TABLE 2Natural history of stage I twin-twin transfusion syndrome19Bebbington M.W. Tiblad E. Huesler-Charles M. Wilson R.D. Mann S.E. Johnson M.P. Outcomes in a cohort of patients with stage I twin-to-twin transfusion syndrome.Ultrasound Obstet Gynecol. 2010; 36 (Level II-2): 48-51Crossref PubMed Scopus (45) Google Scholar, 20Rossi C. D'Addario V. Survival outcomes of twin-twin transfusion syndrome in stage I: a systematic review of the literature.Am J Perinatol. 2012, July 26; ([epub ahead of print]. Level II-1)PubMed Google Scholar, 21Meriki N. Smoleniec J. Challis D. Welsh A.W. Immediate outcome of twin-twin transfusion syndrome following selective laser photocoagulation of communicating vessels at the NSW fetal therapy center.Aust N Z J Obstet Gynaecol. 2010; 50 (Level II-2): 112-119Crossref PubMed Scopus (30) Google ScholarStageIncidence of progression to higher stageIncidence of resolution, regression to lower stage, or stabilityOverall survivalI6/39 (15%)33/39 (85%)102/118 (86%)SMFM. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013. Open table in a new tab SMFM. Twin-twin transfusion syndrome. Am J Obstet Gynecol 2013. The primary etiologic problem underlying TTTS is thought to lie within the architecture of the placenta, as intertwin vascular connections within the placenta are critical for the development of TTTS. Virtually all MCDA placentas have anastomoses that link the circulations of the twins, yet not all MCDA twins develop TTTS. There are 3 main types of anastomoses in monochorionic placentas: venovenous (VV), arterioarterial (AA), and arteriovenous (AV). AV anastomoses are found in 90-95% of MCDA placentas, AA in 85-90%, and VV in 15-20%.28De Paepe M.E. Shapiro S. Greco D. et al.Placental markers of twin-to-twin transfusion syndrome in diamniotic-monochorionic twins: a morphometric analysis of deep artery-to-vein anastomoses.Placenta. 2010; 31 (Level II-3): 269-276Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar, 29Nikkels P.G. Hack K.E. van Gemert M.J. Pathology of twin placentas with special attention to monochorionic twin placentas.J Clin Pathol. 2008; 61 (Level II-2): 1247-1253Crossref PubMed Scopus (83) Google Scholar Both AA and VV anastomoses are direct superficial connections on the surface of the placenta with the potential for bidirectional flow (Figure 4). In AV anastomoses, while the vessels themselves are on the surface of the placenta, the actual anastomotic connections occur in a cotyledon, deep within the placenta (Figure 4). AV anastomoses can result in unidirectional flow from one twin to the other, and if uncompensated, may lead to an imbalance of volume between the twins. Unlike AA and VV, which are direct vessel-to-vessel connections, AV connections are linked through large capillary beds deep within the cotyledon. AV anastomoses are usually multiple and overall balanced in both directions so that TTTS does not occur. While the number of AV anastomoses from donor to recipient may be important, their size as well as placental resistance likely influences the volume of intertwin transfusion that occurs.30Wee L.Y. Sullivan M. Humphries K. Fisk N.M. Longitudinal blood flow in shared (arteriovenous anastomoses) and non-shared cotyledons in monochorionic placentae.Placenta. 2007; 28 (Level II-2): 516-522Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar Placentas in twins affected with TTTS are reportedly more likely to have VV, but less likely to have AA anastomoses.28De Paepe M.E. Shapiro S. Greco D. et al.Placental markers of twin-to-twin transfusion syndrome in diamniotic-monochorionic twins: a morphometric analysis of deep artery-to-vein anastomoses.Placenta. 2010; 31 (Level II-3): 269-276Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar It is thought that these bidirectional anastomoses may compensate for the unidirectional flow through AV connections, thereby preventing the development of TTTS or decreasing its severity when it does occur.31Tan T.Y. Taylor M.J. Wee L.Y. Vanderheyden T. Wimalasundera R. Fisk N.M. Doppler for artery-artery anastomosis and stage-independent survival in twin-twin transfusion.Obstet Gynecol. 2004; 103 (Level II-3): 1174-1180Crossref PubMed Scopus (55) Google Scholar Mortality is highest in the absence of AA and lowest when these anastomoses are present (42% vs 15%).29Nikkels P.G. Hack K.E. van Gemert M.J. Pathology of twin placentas with special attention to monochorionic twin placentas.J Clin Pathol. 2008; 61 (Level II-2): 1247-1253Crossref PubMed Scopus (83) Google Scholar However, the presence of AA is not completely protective, as about 25-30% of TTTS cases may also have these anastomoses.32Diehl W. Hecher K. Zikulnig L. Vetter M. Hackeloer B.J. Placental vascular anastomoses visualized during fetoscopic laser surgery in severe mid-trimester twin-twin transfusion syndrome.Placenta. 2001; 22 (Level II-3): 876-881Abstract Full Text PDF PubMed Scopus (97) Google Scholar The imbalance of blood flow through the placental anastomoses leads to volume depletion in the donor twin, with oliguria and oligohydramnios, and to volume overload in the recipient twin, with polyuria and polyhydramnios. There also appear to be additional factors beyond placental morphology, such as complex interactions of the renin-angiotensin system in the twins,33Mahieu-Caputo D. Dommergues M. Delezoide A.L. et al.Twin-to-twin transfusion syndrome: role of the fetal renin-angiotensin system.Am J Pathol. 2000; 156 (Level II-3): 629-636Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar, 34Fisk N.M. Duncombe G.J. Sullivan M.H. The basic and clinical science of twin-twin transfusion syndrome.Placenta. 2009; 30 (Level II-3): 379-390Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar, 35Galea P. Barigye O. Wee L. Jain V. Sullivan M. Fisk N.M. The placenta contributes to activation of the renin angiotensin system in twin-twin transfusion syndrome.Placenta. 2008; 29 (Level II-3): 734-742Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar involved in the development of this disorder. All women with a twin pregnancy should be offered an ultrasound examination at 10-13 weeks of gestation to assess viability, chorionicity, crown-rump length, and nuchal translucency. TTTS usually presents in the second trimester, and is a dynamic condition that can remain stable throughout gestation, occasionally regress spontaneously, progress slowly over a number of weeks, or develop quickly within a period of days with rapid deterioration in the well-being of the twins. There have been no ran
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