Spontaneous twin anemia--polycythemia sequence complicated by recipient placental vascular thrombosis and hydrops fetalis

Twin anemia--polycythemia sequence (TAPS) is an atypical form of twin--twin transfusion syndrome (TTTS) that presents as a large intertwin hemoglobin difference with one twin developing anemia and the other developing polycythemia, without oligohydramnios--polyhydramnios sequence (Lopriore et al., Placenta 2007;28:47--51). The prenatal diagnostic criteria for TAPS require that the middle cerebral artery-peak systolic velocity (MCA-PSV) measure greater than 1.5 multiples of median (MoM) in the donor twin and less than 0.8 MoM in the recipient twin (Robyr et al., Am J Obstet Gynecol 2006;194:796--803; Klaritsch et al., Ultrasound Obstet Gynecol 2009;34:149--154; Mari et al., N Engl Med 2000;342:9--14). The presumed etiology of TAPS involves the presence of small caliber arteriovenous anastomoses, which generate a slow transfusional process allowing for hemodynamic compensation (Lopriore et al., Placenta 2007;28:47--51; Lopriore et al., Placenta 2009;30:223--225; Lewi et al., Am J Obstet Gynecol 2006;194:790--795; Lopriore et al., Am J Obstet Gynecol 2008;112:753--758; Van den Wijngaard et al., Placenta 2007;28:611--615). The resulting polycythemia in the recipient twin is a risk factor for fetal and placental thrombosis (Van den Wijngaard et al., Am J Physiol 2005;288:R799--R814). We present a case of spontaneous TAPS complicated by a large placental vessel thrombosis and hydrops fetalis. Treatment via selective laser photocoagulation of communicating vessels (SLPCV) resulted in normalization of the MCA-PSV discordance.