Anomalies of the placenta and umbilical cord in twin gestations
2015; Elsevier BV; Volume: 213; Issue: 4 Linguagem: Inglês
10.1016/j.ajog.2015.06.054
ISSN1097-6868
AutoresCorinne Hubinont, Liesbeth Lewi, Pierre Bernard, Étienne Marbaix, Frédéric Debiève, Eric Jauniaux,
Tópico(s)Prenatal Screening and Diagnostics
ResumoThe frequency of twin gestations has increased over the last few decades, mainly due to maternal age at childbearing, and the use of assisted reproductive technologies. Twins are at higher risk of aneuploidy, structural anomalies, and placental abnormalities. Some of the placental and umbilical cord abnormalities found in twin gestations are nonspecific and can be found in singleton gestations (ie, placenta previa, placental abruption, single umbilical artery, velamentous cord insertion, vasa previa, etc). However, other anomalies are unique to twin gestations, and are mainly associated with monochorionic twins–these include intraplacental anastomosis and cord entanglement. Most of these conditions can be diagnosed with ultrasound. An accurate and early diagnosis is important in the management of twin gestations. Determination of chorionicity, amnionicity, and the identification of placental anomalies are key issues for the adequate management of twin pregnancies. Pathologic placental examination after delivery can help in assessing the presence of placental and umbilical cord abnormalities, as well as providing information about chorionicity and gaining insight into the potential mechanisms of disease affecting twin gestations. The frequency of twin gestations has increased over the last few decades, mainly due to maternal age at childbearing, and the use of assisted reproductive technologies. Twins are at higher risk of aneuploidy, structural anomalies, and placental abnormalities. Some of the placental and umbilical cord abnormalities found in twin gestations are nonspecific and can be found in singleton gestations (ie, placenta previa, placental abruption, single umbilical artery, velamentous cord insertion, vasa previa, etc). However, other anomalies are unique to twin gestations, and are mainly associated with monochorionic twins–these include intraplacental anastomosis and cord entanglement. Most of these conditions can be diagnosed with ultrasound. An accurate and early diagnosis is important in the management of twin gestations. Determination of chorionicity, amnionicity, and the identification of placental anomalies are key issues for the adequate management of twin pregnancies. Pathologic placental examination after delivery can help in assessing the presence of placental and umbilical cord abnormalities, as well as providing information about chorionicity and gaining insight into the potential mechanisms of disease affecting twin gestations. With the development of new assisted reproductive techniques (ART) in the late 1970s, multiple gestation pregnancy rates have increased markedly around the world. In the United States, the rate of twin pregnancies has stabilized at 32 per 1000 births in 2006.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar The latest Centers for Disease Control and Prevention report on ART surveillance indicates that 43% of ART-conceived infants in 2011 in the United States were twins.2Sunderam S. Kissin D.M. Crawford S.B. Folger S.G. Jamieson D.J. Barfield W.D. Centers for Disease Control and Prevention (CDC)Assisted reproductive technology surveillance–United States, 2011.MMWR Surveill Summ. 2014; 63: 1-28PubMed Google Scholar Twinning is associated with higher incidence of perinatal risks for both mothers and fetuses compared to singleton pregnancies. The main risks are early and late miscarriage, preeclampsia, antepartum bleeding, postpartum hemorrhage, preterm delivery, intrauterine growth restriction (IUGR), and stillbirths.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 2Sunderam S. Kissin D.M. Crawford S.B. Folger S.G. Jamieson D.J. Barfield W.D. Centers for Disease Control and Prevention (CDC)Assisted reproductive technology surveillance–United States, 2011.MMWR Surveill Summ. 2014; 63: 1-28PubMed Google Scholar, 3The ESHRE Capri Workshop GroupMultiple gestation pregnancy.Hum Reprod. 2000; 15: 1856-1864Crossref PubMed Google Scholar, 4Jauniaux E. Ben-Ami I. Maymon R. Do assisted-reproduction twin pregnancies require additional antenatal care?.Reprod Biomed Online. 2013; 26: 107-119Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar Twins are also more prone to birth asphyxia, hyaline membrane disease, respiratory disorders, seizures, and long-term developmental morbidity.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 2Sunderam S. Kissin D.M. Crawford S.B. Folger S.G. Jamieson D.J. Barfield W.D. Centers for Disease Control and Prevention (CDC)Assisted reproductive technology surveillance–United States, 2011.MMWR Surveill Summ. 2014; 63: 1-28PubMed Google Scholar, 3The ESHRE Capri Workshop GroupMultiple gestation pregnancy.Hum Reprod. 2000; 15: 1856-1864Crossref PubMed Google Scholar, 4Jauniaux E. Ben-Ami I. Maymon R. Do assisted-reproduction twin pregnancies require additional antenatal care?.Reprod Biomed Online. 2013; 26: 107-119Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar Prematurity and its complications is the single most important cause of perinatal morbidity and mortality in multiple pregnancies.6Conde Agudelo A. Romero R. Prediction of preterm birth in twin gestations using biophysical and biochemical tests.Am J Obstet Gynecol. 2014; 211: 583-595Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar Overall, perinatal mortality rates are reported to be 4-fold higher for twins than for singletons.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 3The ESHRE Capri Workshop GroupMultiple gestation pregnancy.Hum Reprod. 2000; 15: 1856-1864Crossref PubMed Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar Most of these complications are directly or indirectly associated with placental or umbilical cord disorders.5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar Twin pregnancies are obviously at higher risks for birth defects than singleton due to the development of 2 fetuses instead of 1.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar, 8Davies M.J. Moore V.M. Willson K.J. et al.Reproductive technologies and the risk of birth defects.N Engl J Med. 2012; 366: 1803-1813Crossref PubMed Scopus (569) Google Scholar Cohort studies have suggested that in vitro fertilization (IVF) could be associated with higher incidence of birth defects.7Jauniaux E.R.M. Multiple gestation pregnancy after assisted reproductive technology.in: Jauniaux E.R.M. Risk R.M.B. Pregnancy after assisted reproductive technology. Cambridge University Press, Cambridge2012: 82-92Crossref Scopus (3) Google Scholar, 8Davies M.J. Moore V.M. Willson K.J. et al.Reproductive technologies and the risk of birth defects.N Engl J Med. 2012; 366: 1803-1813Crossref PubMed Scopus (569) Google Scholar However, the lack of information on the etiology of the infertility, chorionicity, maternal preexisting medical conditions, parental smoking status, and social environments in most studies hampers the interpretation of the corresponding data.7Jauniaux E.R.M. Multiple gestation pregnancy after assisted reproductive technology.in: Jauniaux E.R.M. Risk R.M.B. Pregnancy after assisted reproductive technology. Cambridge University Press, Cambridge2012: 82-92Crossref Scopus (3) Google Scholar A recent large Australian cohort study showed that the increased risk of birth defects associated with IVF is no longer significant after adjustment for parental factors.8Davies M.J. Moore V.M. Willson K.J. et al.Reproductive technologies and the risk of birth defects.N Engl J Med. 2012; 366: 1803-1813Crossref PubMed Scopus (569) Google Scholar However, placenta previa and velamentous cord insertion (VCI) are more common in singleton IVF than in spontaneous pregnancies suggesting the incidence of placental and cord anomalies can be influenced by the mode of conception.4Jauniaux E. Ben-Ami I. Maymon R. Do assisted-reproduction twin pregnancies require additional antenatal care?.Reprod Biomed Online. 2013; 26: 107-119Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 7Jauniaux E.R.M. Multiple gestation pregnancy after assisted reproductive technology.in: Jauniaux E.R.M. Risk R.M.B. Pregnancy after assisted reproductive technology. Cambridge University Press, Cambridge2012: 82-92Crossref Scopus (3) Google Scholar Development, position, and vascularity abnormalities of the placenta and the umbilical cord can impact significantly perinatal morbidity and mortality. The aim of this review is to provide an outline of these anomalies associated with the twinning process and discuss the corresponding pathophysiology and diagnostic features. Most of these pathologies can be diagnosed in utero by routine ultrasound examination and should be an integral part of prenatal investigations in twins.4Jauniaux E. Ben-Ami I. Maymon R. Do assisted-reproduction twin pregnancies require additional antenatal care?.Reprod Biomed Online. 2013; 26: 107-119Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar, 9McNamara HC, Kane SC, Craig JM, Short RV, Umstad MP. A review of the mechanisms and evidence for typical and atypical twinning. Am J Obstet Gynecol (in press).Google Scholar For a better understanding of the pathogenesis, it is essential to confirm the prenatal diagnosis with a detailed histopathological placenta examination at birth. Placental and cord pathologies are traditionally divided into primary or congenital anomalies such as tumors and secondary anomalies such as thrombosis. For the purpose of our review, we have analyzed these anomalies according their specific and nonspecific association with twin pregnancies. Zygosity and chorionicity are distinct entities. A dichorionic (DC)-diamniotic (DA) placenta can be found in both monozygotic (MZ) and dizygotic twins whereas a single or monochorionic (MC) placenta mass is mainly associated with MZ twins.10Krauss FT, Redline RW, Gersell DJ, Nelson DM, Dicke JM. Multiple pregnancy. In: Placental pathology. Atlas of nontumor pathology, Edt. American Registry of Pathology, Washington, DC: 2004:249-82.Google Scholar Zygosity or twins classification based on a double or a single fertilization cannot be predicted in DC similar gender twins.11Scardo J.A. Ellings J.M. Newman R.B. Prospective determination of chorionicity, amniocity and zygosity in twin gestations.Am J Obstet Gynecol. 1995; 173: 1376-1380Abstract Full Text PDF PubMed Scopus (79) Google Scholar The low incidence of MZ twinning is constant worldwide and seems independent of environmental factors.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 2Sunderam S. Kissin D.M. Crawford S.B. Folger S.G. Jamieson D.J. Barfield W.D. Centers for Disease Control and Prevention (CDC)Assisted reproductive technology surveillance–United States, 2011.MMWR Surveill Summ. 2014; 63: 1-28PubMed Google Scholar However, ART and mainly IVF increase both the incidence of MZ but also MC twins.3The ESHRE Capri Workshop GroupMultiple gestation pregnancy.Hum Reprod. 2000; 15: 1856-1864Crossref PubMed Google Scholar, 4Jauniaux E. Ben-Ami I. Maymon R. Do assisted-reproduction twin pregnancies require additional antenatal care?.Reprod Biomed Online. 2013; 26: 107-119Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar Zygosity is generally established postnatally using genetic tests on umbilical cord blood. Quantitative fluorescent polymerase chain reaction amplification of microsatellite markers has been performed antenatally on fetal/placental cells obtained from amniocentesis or chorionic villous sampling for scientific purposes.12Cirigliano V. Canadas P. Plaja A. et al.Rapid prenatal diagnosis of aneuploidies and zygosity in multiple pregnancies by amniocentesis with single insertion of the needle and quantitative fluorescent PCR.Prenat Diagn. 2003; 23: 629-633Crossref PubMed Scopus (21) Google Scholar Noninvasive prenatal determination of twin zygosity using maternal plasma free fetal DNA sequencing similar to that used for the aneuploidy testing has recently been reported.13Qu J.Z. Leung T.Y. Liao G.J. et al.Non invasive prenatal diagnosis of twin zygosity by maternal plasma DNA analysis.Clin Chem. 2013; 59: 427-435Crossref PubMed Scopus (50) Google Scholar Independently of the conception mode, the fetal, placental, and cord anomalies risk depends mainly on the chorionicity and amnionicity in twins.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 4Jauniaux E. Ben-Ami I. Maymon R. Do assisted-reproduction twin pregnancies require additional antenatal care?.Reprod Biomed Online. 2013; 26: 107-119Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar, 14Kristiansen M. Joensen B. Ekelund C. Petersen O. Sandager P. with the Danish Fetal Medicine Study GroupPerinatal outcome after first-trimester risk assessment in monochorionic and dichorionic twin pregnancies: a population-based register study.BJOG. 2015; ([Epub ahead of print])https://doi.org/10.1111/1471-0528.13326Crossref PubMed Scopus (13) Google Scholar Overall, perinatal mortality is around 11% in MC twins compared to 5.0% in DC twins.1Chauhan S. Scardo J. Hayes E. Abuhamad A. Berghella V. Twins: prevalence, problems, and preterm births.Am J Obstet Gynecol. 2010; 203: 305-315Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 5Steenhaut P. Hubinont C. Perinatal mortality in multiple pregnancy.in: Ezechi O.C. Pettersson K.O. Perinatal mortality. In Tech Europe, Croatia2015Google Scholar, 14Kristiansen M. Joensen B. Ekelund C. Petersen O. Sandager P. with the Danish Fetal Medicine Study GroupPerinatal outcome after first-trimester risk assessment in monochorionic and dichorionic twin pregnancies: a population-based register study.BJOG. 2015; ([Epub ahead of print])https://doi.org/10.1111/1471-0528.13326Crossref PubMed Scopus (13) Google Scholar Monoamniotic (MA) twins are rare (1% of MZ twins) but associated with the highest morbidity and mortality rate of all different types of twinning.9McNamara HC, Kane SC, Craig JM, Short RV, Umstad MP. A review of the mechanisms and evidence for typical and atypical twinning. Am J Obstet Gynecol (in press).Google Scholar, 15Constantine S. Wilkinson C. Double trouble: the importance of reporting chorionicity and amnionicity in twin pregnancy ultrasound reports.J Med Imaging Radiat Oncol. 2015; 59: 66-69Crossref PubMed Scopus (5) Google Scholar, 16Van Mieghem T. De Heus R. Lewi L. et al.Prenatal management of monoamniotic twin pregnancies.Obstet Gynecol. 2014; 124: 498-506Crossref PubMed Scopus (51) Google Scholar An early determination of chorionicity and amnionicity is therefore essential to optimize the management pathways in twin pregnancies.17Hubinont C. Santolaya-Forgas J. A systematic approach to first-trimester ultrasound assessment of twins.Am J Perinatol. 2010; 27: 595-598Crossref PubMed Scopus (4) Google Scholar, 18Bora S.A. Papageorghiou A.T. Bottomley C. Kirk E. Bourne T. Reliability of transvaginal ultrasonography at 7-9 weeks' gestation in the determination of chorionicity and amnionicity in twin pregnancies.Ultrasound Obstet Gynecol. 2008; 32: 618-621Crossref PubMed Scopus (28) Google Scholar, 19Carroll S.G. Soothill P.W. Abdel-Fattah S.A. Porter H. Montague I. Kyle P.M. Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation.BJOG. 2002; 109: 182-186PubMed Google Scholar, 20Blumenfeld Y.J. Momirova V. Rouse D.J. et al.Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units NetworkAccuracy of sonographic chorionicity classification in twin gestations.J Ultrasound Med. 2014; 33: 2187-2192Crossref PubMed Scopus (24) Google Scholar The optimal window to determine chorionicity in twins with 98% accuracy is at 7-9 weeks of gestation.18Bora S.A. Papageorghiou A.T. Bottomley C. Kirk E. Bourne T. Reliability of transvaginal ultrasonography at 7-9 weeks' gestation in the determination of chorionicity and amnionicity in twin pregnancies.Ultrasound Obstet Gynecol. 2008; 32: 618-621Crossref PubMed Scopus (28) Google Scholar Accuracy may be higher for DC twins than MC twins and is related to the gestational age at which the sonographic appearance of the amniotic sac develops. Ultrasound examination of twin pregnancies at 10-14 weeks of gestation predicts chorionicity with a high degree of accuracy using a combination of the number of placentas, lambda and T signs, and intertwin membrane thickness.17Hubinont C. Santolaya-Forgas J. A systematic approach to first-trimester ultrasound assessment of twins.Am J Perinatol. 2010; 27: 595-598Crossref PubMed Scopus (4) Google Scholar, 18Bora S.A. Papageorghiou A.T. Bottomley C. Kirk E. Bourne T. Reliability of transvaginal ultrasonography at 7-9 weeks' gestation in the determination of chorionicity and amnionicity in twin pregnancies.Ultrasound Obstet Gynecol. 2008; 32: 618-621Crossref PubMed Scopus (28) Google Scholar, 19Carroll S.G. Soothill P.W. Abdel-Fattah S.A. Porter H. Montague I. Kyle P.M. Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation.BJOG. 2002; 109: 182-186PubMed Google Scholar Two distinct placental masses and different fetal gender indicate DC. When only 1 placental mass is visible on ultrasound, the presence of a lambda sign at the insertion of the intertwin membranes is an accurate predictor for DC whereas T sign is the most reliable indicator of MC (Figure 1).17Hubinont C. Santolaya-Forgas J. A systematic approach to first-trimester ultrasound assessment of twins.Am J Perinatol. 2010; 27: 595-598Crossref PubMed Scopus (4) Google Scholar, 18Bora S.A. Papageorghiou A.T. Bottomley C. Kirk E. Bourne T. 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Rouse D.J. et al.Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units NetworkAccuracy of sonographic chorionicity classification in twin gestations.J Ultrasound Med. 2014; 33: 2187-2192Crossref PubMed Scopus (24) Google Scholar Measurements of the intertwin membrane thickness and membrane layer count are associated with a lower sensitivity and specificity than the ultrasound features used earlier in pregnancy but can be useful to determine chorionicity during the second trimester of pregnancy when the insertion of the intertwin is less clear.20Blumenfeld Y.J. Momirova V. Rouse D.J. et al.Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units NetworkAccuracy of sonographic chorionicity classification in twin gestations.J Ultrasound Med. 2014; 33: 2187-2192Crossref PubMed Scopus (24) Google Scholar MA is determined by the absence of a dividing membrane between the amniotic sacs.11Scardo J.A. Ellings J.M. Newman R.B. Prospective determination of chorionicity, amniocity and zygosity in twin gestations.Am J Obstet Gynecol. 1995; 173: 1376-1380Abstract Full Text PDF PubMed Scopus (79) Google Scholar, 15Constantine S. Wilkinson C. Double trouble: the importance of reporting chorionicity and amnionicity in twin pregnancy ultrasound reports.J Med Imaging Radiat Oncol. 2015; 59: 66-69Crossref PubMed Scopus (5) Google Scholar, 17Hubinont C. Santolaya-Forgas J. A systematic approach to first-trimester ultrasound assessment of twins.Am J Perinatol. 2010; 27: 595-598Crossref PubMed Scopus (4) Google Scholar MA should be suspected at 10-14 weeks in the presence of a single amniotic sac and closely inserted umbilical cords (Figure 2). The number of yolk sacs is not always an accurate sonographic sign of amnionicity.21Shen O. Samueloff A. Beller U. Rabinowitz R. Number of yolk sacs does not predict amniocity in early first-trimester monochorionic multiple gestations.Ultrasound Obstet Gynecol. 2006; 27: 53-56Crossref PubMed Scopus (33) Google Scholar, 22Murakoshi T. Ishii K. Matsushita M. Shinno T. Naruse H. Torii Y. Monochorionic monoamniotic twin pregnancies with two yolk sacs may not be a rare finding: a report of two cases.Ultrasound Obstet Gynecol. 2010; 36: 384-386Crossref PubMed Scopus (17) Google Scholar Nearly all MC placentas have vascular connections or anastomoses between the 2 umbilical-placental circulations.23Benirschke K. 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Three different types of anastomoses have been described: arterioarterial (AA), arteriovenous (AV), and venovenous (VV) (Figure 4).Figure 4Types, characteristics, physiopathological effects, and incidence of vascular anastomoses in monochorionic placentasShow full captionAV, arteriovenous; IUFD, intrauterine fetal death; MC, monochorionic; TAPS, twin anemia polycythemia sequence; TRAP, twin reversed arterial perfusion sequence; TTTS, twin to twin transfusion syndrome.Hubinont. Placental and cord disorders in twin gestations. Am J Obstet Gynecol 2015.View Large Image Figure ViewerDownload Hi-res image Download (PPT) AV, arteriovenous; IUFD, intrauterine fetal death; MC, monochorionic; TAPS, twin anemia polycythemia sequence; TRAP, twin reversed arterial perfusion sequence; TTTS, twin to twin transfusion syndrome. Hubinont. Placental and cord disorders in twin gestations. Am J Obstet Gynecol 2015. Their role in twin's morbidity is well established since early studies have suggested that in twin-twin transfusion syndrome (TTTS) there is an important blood flow transfer through unidirectional AV anastomoses with an insufficient compensatory counter-transfusion.25Bajoria R. Wigglesworth J. Fisk N.M. Angioarchitecture of monochorionic placentas in relation to the twin-twin transfusion syndrome.Am J Obstet Gynecol. 1995; 172: 856-863Abstract Full Text PDF PubMed Scopus (247) Google Scholar, 26Bermúdez C. Becerra C.H. Bornick P.W. Allen M.H. Arroyo J. Quintero R.A. Placental types and twin-twin transfusion syndrome.Am J Obstet Gynecol. 2002; 187: 489-494Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar, 28de Villiers S.F. Slaghekke F. Middeldorp J.M. Walther F.J. Oepkes D. Lopriore E. Arterio-arterial vascular anastomoses in monochorionic placentas with and without twin-twin transfusion syndrome.Placenta. 2012; 33: 652-654Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar, 29Fisk N.M. Duncombe G.J. Sullivan M.H. The basic and clinical science of twin-twin transfusion syndrome.Placenta. 2009; 30: 379-390Abstract Full Text Full Text PDF PubMed Scopus (80) Google Scholar These anastomoses are generally superficial and bidirectional.24Lewi L. Deprest J. Hecher K. The vascular anastomoses in monochorionic twin pregnancies and their clinical consequences.Am J Obstet Gynecol. 2013; 208: 19-30Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar, 27De Paepe M.E. Examination of the twin placenta.Semin Perinatol. 2015; 39: 27-35Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar Their frequency varies but their presence seems to be associated with a protective effect for many of the complications of MC (Figure 4). A recent case-control series has found that AA anastomoses are present in 37% of TTTS placentas compared to 91% in control non-TTTS placentas (P < .001).28de Villiers S.F. Slaghekke F. Middeldorp J.M. Walther F.J. Oepkes D. Lopriore E. Arterio-arterial vascular anastomoses in monochorionic placentas with and without twin-twin transfusion syndrome.Placenta. 2012; 33: 652-654Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar AA anastomoses are also less frequent in twin anemia-polycythemia sequence (TAPS). TAPS is a particular form of intertwin transfusion imbalance, which is characterized by a difference in hemoglobin without the amniotic fluid discordance typical for chronic TTTS.30de Villiers S. Slaghekke F. Middeldorp J.M. et al.Arterio-arterial vascular anastomoses in monochorionic twin placentas with and without twin anemia-polycythemia sequence.Placenta. 2012; 33: 227-229Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar When AA anastomoses are present in TAPS, they have a smaller diameter than those found in placentas from control twin pregnancies (Figure 5).30de Villiers S. Slaghekke F. Middeldorp J.M. et al.Arterio-arterial vascular anastomoses in monochorionic twin placentas with and without twin anemia-polycythemia sequence.Placenta. 2012; 33: 227-229Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar, 31Van Meir H. Slaghekke F. Lopriore E. Van Wijngaarden W.J. Arterio-arterial anastomoses do not prevent the development of twin anemia-polycythemia sequence.Placenta. 2010; 31: 163-165Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar AA anastomoses can be demonstrated by color Doppler ultrasound imaging and are characterized by cyclic changes in systolic velocities with intermittent reversal of end-diastolic velocities.32Hecher K. Jauniaux E. Campbell S. Deane C. Nicolaides K. Artery-to-artery anastomosis in monochorionic twins.Am J Obstet Gynecol. 1994; 171: 570
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