Twin-twin transfusion syndrome (TTTS)

The etiology of TTTS is connected with the architecture of the placenta, and intertwine vascular connections known as anastomoses within the placenta. Actually all MC placentas have anastomoses that connect the fetal circulations. Fortunately, not all MC twins develop TTTS. Three main types of anastomoses might be distinguished: venovenous (VV), arterioarterial (AA), and arteriovenous (AV). The imbalance of blood flow through the placental anastomoses leads to volume depletion in the donor twin, with oliguria and oligohydramnios, and to volume overload in the recipient twin, with polyuria and polyhydramnios. There also appear to be additional factors beyond placental morphology, such as complex interactions of the renin-angiotensin system in the twins involved in the development of this disorder. There are no randomized trials to evaluate the effectiveness of antenatal monitoring or pregnancies complicated by TTTS. Weekly monitoring of the umbilical artery Doppler flow and MVP of amniotic fluid of each fetus may be considered. The evidence for effectiveness of serial (eg, weekly or twice/wk) nonstress tests, biophysical profiles, and other antenatal testing modalities is insufficient to make a recommendation, but these tests can be considered. The management options described for TTTS include expectant management, amnioreduction, intentional septostomy of the intervening membrane, fetoscopic laser photocoagulation of placental anastomoses, and selective reduction. There are no clinical trials regarding optimal timing of delivery for TTTS pregnancies. This depends on several factors, including disease stage and severity, progression, effect of interventions, and results of antenatal testing. Recommendations regarding timing of delivery with TTTS vary, with some endorsing planned preterm delivery as early as 32-34 weeks, and others individualizing care and allowing gestation to progress to 34-37 weeks, particularly in cases of mild disease (eg. stages I and II) with reassuring surveillance.