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Pathology of twin placentas with special attention to monochorionic twin placentas.
  1. Peter G.J. Nikkels (p.g.j.nikkels{at}
  1. University Medical Center Utrecht, Netherlands
    1. Karien E.A Hack
    1. Department of obstetrics, University Medical Center Utrecht, Netherlands
      1. Martin J.C. van Gemert
      1. Laser center, Academic Medical Center Amsterdam, Netherlands


        The risk of perinatal morbidity and mortality in twins is 3-7 times higher as compared to singletons. In comparison to dichorionic twins, monochorionic twins are at increased risk for perinatal mortality and serious morbidity compared to dichorionic twins. In both type of twins growth discordance can occur. Discordant growth of dichorionic twins could be due to differences in placental mass or due to differences in placental parenchymal lesions, whereas birth weight discordancy in monochorionic twins is caused by placental vascular anastomoses. In this review the different types of complications (acardiac twins, acute and chronic twin-twin transfusion syndrome) due to different combinations of vascular anastomoses is discussed in relation with a computer model developed to get more insight into the development of the twin-twin transfusion syndrome. The angioarchitecture of 395 monochorionic twin placentas were studied. Mortality was highest in the absence of an arterio-arterial anastomoses (42 %) and lowest in the presence of an A-A anastomoses (15 %). If mortality occurred, pregnancies with double mortality usually had an arterio-arterial anastomoses. If pregnancies were complicated by one death, a veno-venous anastomosis is more likely to be present. In conclusion monochorionc twin pregnancies are a high risk pregnancy with a high chance on both mortality and morbidity and placental characteristics are a major contributor to adverse outcome in these pregnancies.

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