Twin anemia-polycythemia sequence (TAPS) is a novel form of chronic feto-fetal transfusion, characterized by large inter-twin hemoglobin differences, without signs of twin oligo-polyhydramnios sequence (TOPS).
The pathogenesis of TAPS is based on the presence of few, minuscule anastomoses at the placental surface (diameter <1mm) allowing a slow transfusion of blood from the donor to the recipient and leading gradually to highly discordant Hb levels.
TAPS may occur spontaneously or after laser surgery for TTTS (post-laser form). Spontaneous TAPS complicates approximately 1 to 5% of monochorionic twin pregnancies, whereas the post-laser TAPS occurs in 1 to 16% of TTTS cases treated with laser.
The optimal management in TAPS is not clear, and includes expectant management, induction of labor, intrauterine blood transfusion (intravenous and/or intraperitoneal, with or without partial exchange transfusion), selective feticide or fetoscopic laser surgery.
The outcome in TAPS is not well known. International cooperation between fetal centers using a web-based TAPS registry is needed to improve our knowledge on the on the short- and long-term outcome in TAPS cases and determine the optimal management.