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The twin-twin transfusion syndrome.

Twin-twin transfusion syndrome is a complication of monozygotic-monochorionic twinning with serious perinatal implications. An extensive literature review revealed that our current understanding of the anatomy and pathogenesis of the syndrome has not changed over the last 3 decades. However, modern diagnostic modalities, such as sonography and Doppler studies, allow antenatal diagnosis and therefore may change the current definition of the syndrome. Based on these data, a new composite definition of the syndrome is suggested. This definition includes the following criteria: 1) sonographic signs (inter-twin differences in abdominal circumference greater than 18 mm, polyhydramnios-oligohydramnios, and signs of monozygosity), 2) Doppler velocimetry of the umbilical arteries (inter-twin difference in systolic/diastolic ratios above 0.4), 3) demonstration of a transplacental vascular shunt, 4) inter-twin birth weight difference of 15% or more, and 5) inter-twin hemoglobin difference of 5 g/dL or more. In addition, prenatal diagnosis may help in the management of this complication, and it seems that intrauterine treatment of the placental vascular anomalies may be more effective than other antenatal therapeutic options.