twin could die. This procedure is associated with a 66% survival rate of at least one fetus, with a 15% risk of cerebral palsy, and average delivery occurring at 29 weeks' gestation. Septostomy, or iatrogenic disruption of the dividing membrane This procedure involves the tearing of the dividing membrane between fetuses such that the amniotic fluid of both twins mixes, under the assumption that pressure is different in either amniotic sac and that its equilibration will ameliorate progression of the disease. It has not been proven that pressures are different in either amniotic sac. Use of this procedure can preclude use of other procedures as well as make difficult the monitoring of disease progression. In addition, tearing the dividing membrane has contributed to cord entanglement and demise of fetuses through physical complications. Adjustment of blood supply Laser therapy This procedure involves endoscopic surgery using laser to interrupt the vessels that allow exchange of blood between fetuses under the assumption that the unequal sharing of blood through these vascular communications leads to unequal levels of amniotic fluid. Each fetus remains connected to its primary source of blood and nutrition, the placenta, through the umbilical cord. This procedure is conducted once, with the exception of all vessels not having been found. The use of endoscopic instruments allows for short recovery time. This procedure has been associated with 85% survival rate of at least one fetus, with a 6–7% risk of cerebral palsy and average delivery occurring at 32–33 weeks' gestation. Twin anemia–polycythemia sequence (TAPS) may occur after laser surgery for TTTS (post-laser form). The spontaneous form of TAPS complicates approximately 3 to 5% of monochorionic twin pregnancies, whereas the post-laser form occurs in 2 to 13% of TTTS cases. The pathogenesis of TAPS is based on the presence of few, minuscule arterio-venous (AV) placental anastomoses (diameter <1mm) allowing a slow transfusion of blood from the donor to the recipient and leading gradually to highly discordant Hb levels. A 2014 review found that laser coagulation resulted in fewer fetal and perinatal deaths than amnioreduction and septostomy, and recommended its use for all states of TTTS. Umbilical cord occlusion This procedure involves the ligation or otherwise occlusion of the umbilical cord to interrupt the exchange of blood between the fetuses. The procedure is typically offered in cases where one of the fetuses is presumed moribund and endangering the life or health of the other