Selective fetal growth restriction (sFGR) affects about 10–15% of monochorionic (MC) twin pregnancies. When presenting during the second trimester, sFGR is a severe complication, with potentially significant risks of intrauterine demise or neurological adverse outcome for both the growth-restricted and the normally grown [1–9] fetuses. Unequal placental sharing (Figure 37.1), often associated with velamentous cord insertion, is the main cause of the development of sFGR in MC twins [10–14]. The natural history of sFGR in MC twins depends both on the discordance in placental territories and on the pattern of placental anastomoses. The blood flow interchange through vascular anastomoses interferes with the natural evolution of placental insufficiency, because the small fetus receives extra oxygen and nutrients from its normally grown co-twin. The pattern of vascular anastomoses, which may differ substantially among MC pregnancies, explains the remarkable differences in clinical course and outcomes that can be observed in pregnancies with similar degrees of fetal weight discordance [1, 12, 15, 16]. Consequently, a large interfetal blood flow interchange will result in a milder clinical course and better outcomes, while placentas with small/few anastomoses and little blood flow interchange will usually be associated with a more severe clinical course. Aside from these, large artery-to-artery (AA) anastomoses connecting the two cords may be present, and also have a strong influence on the clinical evolution.