title: Placental characteristics in monochorionic twins with and without twin anemia-polycythemia sequence.
abstract: OBJECTIVE
  To study the placental angioarchitecture of monochorionic placentas with and without twin anemia-polycythemia sequence.
  
  
  METHODS
  Eligible were all placentas from monochorionic twin gestations, not complicated by twin-to-twin transfusion syndrome and resulting in double survival. The study was conducted at two European Fetal Therapy Centers between 2002 and 2008. Placental angioarchitecture was evaluated using colored dye injection. Diagnosis of twin anemia-polycythemia sequence was based on the presence of large intertwin hemoglobin difference without the degree of amniotic fluid discordance that is required for the diagnosis of twin transfusion syndrome.
  
  
  RESULTS
  Three-hundred thirteen monochorionic twin pregnancies were eligible for the study but placental data could not be completed for 62 placentas (20%). This left 251 monochorionic twin pregnancies of which 11 (4%) fulfilled the criteria for twin anemia-polycythemia sequence. The median number of anastomoses in monochorionic placentas with and without twin anemia-polycythemia sequence was 3 (range: 2-5) and 7 (range: 0-25), respectively (P<.001). Small anastomoses were present in 91% (10/11) of twin anemia-polycythemia sequence-placentas compared with 5% (12/240) of cases without twin anemia-polycythemia sequence (P<.001). Arterioarterial anastomoses were absent in twin anemia-polycythemia sequence-placentas and present in 89% (213/240) of placentas without twin anemia-polycythemia sequence (P<.001).
  
  
  CONCLUSIONS
  Monochorionic twin placentas with twin anemia-polycythemia sequence are characterized by a paucity of anastomoses and the absence of arterioarterial anastomoses. The few anastomoses that are present in twin anemia-polycythemia sequence placentas are mostly small arteriovenous anastomoses.
authors.affiliation: Division of Neonatology, Department of Pediatrics, Leiden University Medical Centre, Leiden, the Netherlands. e.lopriore@lumc.nl
authors.forename: E
authors.initials: E
authors.lastname: Lopriore
authors.forename: J
authors.initials: J
authors.lastname: Deprest
authors.forename: F
authors.initials: F
authors.lastname: Slaghekke
authors.forename: D
authors.initials: D
authors.lastname: Oepkes
authors.forename: J M
authors.initials: JM
authors.lastname: Middeldorp
authors.forename: F P H A
authors.initials: FP
authors.lastname: Vandenbussche
authors.forename: L
authors.initials: L
authors.lastname: Lewi
mesh_terms: D001724:Birth Weight; D002823:Chorion; D004700:Endocrine System Diseases / Q000473:pathology*; D005260:Female; D005330:Fetofetal Transfusion / Q000473:pathology*; D006801:Humans; D007231:Infant, Newborn; D010920:Placenta / Q000098:blood supply / Q000473:pathology*; D011086:Polycythemia / Q000473:pathology*; D011247:Pregnancy; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014427:Twins