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.