Monochorionic (MC) twin pregnancies are at increased risk of serious complications. The higher rate of perinatal mortality and morbidity is related directly to the unique angio-architecture of the MC placenta. All MC placentas have vascular anastomoses connecting the circulations of both fetuses. Imbalanced inter-twin blood flow is the accepted etiology in twin-twin transfusion syndrome (TTTS), of one of the most severe disorders in MC pregnancies.
Recently (2007), a new complication in MC twins has been discovered, termed twin anemia-polycythemia sequence (TAPS). TAPS is a form of chronic feto-fetal transfusion, characterized by large inter-twin hemoglobin (Hb) differences, without signs of twin oligo-polyhydramnios sequence (TOPS)1. TAPS may occur spontaneously or after laser surgery for TTTS (post-laser TAPS). Spontaneous TAPS complicates approximately 1 to 6% of monochorionic twin pregnancies2-5, whereas post-laser TAPS occurs in up to 16% of TTTS cases6-8. The pathogenesis of TAPS is based on the presence of few, minuscule anastomoses at the placental surface (diameter <1mm)9 allowing a slow transfusion of blood from the donor to the recipient and leading gradually to highly discordant Hb levels3.
(1) Lopriore E, Middeldorp JM, Oepkes D, Kanhai HH, Walther FJ, Vandenbussche FP. Twin anemia-polycythemia sequence in two monochorionic twin pairs without oligo-polyhydramnios sequence. Placenta 2007; 28(1):47-51.
(2) Lewi L, Jani J, Blickstein I, Huber A, Gucciardo L, Van Mieghem T 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(5):514-518.
(3) Slaghekke F, Kist WJ, Oepkes D, Pasman SA, Middeldorp JM, Klumper FJ et al. Twin anemia-polycythemia sequence: diagnostic criteria, classification, perinatal management and outcome. Fetal Diagn Ther 2010; 27(4):181-190.
(4) Nakayama S, Ishii K, Kawaguchi H, Hayashi S, Hidaka N, Murakoshi T, Mitsuda N. Perinatal outcome of monochorionic diamniotic twin pregnancies managed from early gestation at a single center. J Obstet Gynaecol Res 2012; 38(4):692-697.
(5) Gucciardo L, Lewi L, Vaast P, Debska M, De Catte L, van Mieghem T, Done E, Devlieger R, Deprest J. Twin anemia polycythemia sequence from a prenatal perspective. Prenat Diagn 2010; 30(5):438-442.
(6) Robyr R, Lewi L, Salomon LJ, Yamamoto M, Bernard JP, Deprest J et al. Prevalence and management of late fetal complications following successful selective laser coagulation of chorionic plate anastomoses in twin-to-twin transfusion syndrome. Am J Obstet Gynecol 2006; 194(3):796-803.
(7) Habli M, Bombrys A, Lewis D, Lim FY, Polzin W, Maxwell R et al. Incidence of complications in twin-twin transfusion syndrome after selective fetoscopic laser photocoagulation: a single-center experience. Am J Obstet Gynecol 2009; 201(4):417.
(8) Slaghekke F, Lopriore E, Lewi L, Middeldorp JM, Zwet van EW, Weingertner AS et al. Fetoscopic laser coagulation of the vascular equator versus selective coagulation for twin-to-twin transfusion syndrome: a randomised trial. Lancet.2014; doi:10.1016/S0140-6736(13)62419-8.
(9) Lopriore E, Deprest J, Slaghekke F, Oepkes D, Middeldorp JM, Vandenbussche FP et al. Placental characteristics in monochorionic twins with and without twin anemia-polycythemia sequence. Obstet Gynecol 2008; 112(4):753-758.