Although Doppler imaging is likely of little to no value in uncomplicated monochorionic twins, serial assessment of the ductus venosus, umbilical artery and vein, and middle cerebral artery may be useful in cases complicated by unequal placental sharing, twin- twin transfusion syndrome, or twin anemia polycythemia sequence [45]. US Echocardiography Fetal Because of the substantial risk of congenital heart disease, there is strong evidence to support the use of fetal echocardiography for all monochorionic twins, regardless of the nuchal translucency measurement [20]. The overall risk of congenital heart disease in monochorionic twins is 2%, double the background risk of a singleton, and increases to 5% in cases of twin-twin transfusion syndrome, particularly among recipient twins [63]. Recipient twins often demonstrate evidence of volume overload with increased pulmonary and aortic velocities, cardiomegaly, and atrioventricular regurgitation, which, over time, can result in biventricular hypertrophy and diastolic dysfunction [64]. Poor right ventricular systolic function can lead to functional right ventricular outflow tract obstruction in up to 10% of recipient twins, which may progress to severe pulmonic stenosis and a poor prognosis [64]. In contrast, recipient twins with normal cardiac function have improved survival [65]. Therefore, in addition to excluding structural heart defects in monochorionic twins, fetal echocardiography with a detailed functional assessment may be useful in identifying cases of twin-twin transfusion syndrome that would benefit from fetoscopic laser therapy and in evaluating the response to treatment.
Nuchal Translucency Evaluation at 11 to 14 Weeks Gestational Age. Although Doppler imaging is likely of little to no value in uncomplicated monochorionic twins, serial assessment of the ductus venosus, umbilical artery and vein, and middle cerebral artery may be useful in cases complicated by unequal placental sharing, twin- twin transfusion syndrome, or twin anemia polycythemia sequence [45]. US Echocardiography Fetal Because of the substantial risk of congenital heart disease, there is strong evidence to support the use of fetal echocardiography for all monochorionic twins, regardless of the nuchal translucency measurement [20]. The overall risk of congenital heart disease in monochorionic twins is 2%, double the background risk of a singleton, and increases to 5% in cases of twin-twin transfusion syndrome, particularly among recipient twins [63]. Recipient twins often demonstrate evidence of volume overload with increased pulmonary and aortic velocities, cardiomegaly, and atrioventricular regurgitation, which, over time, can result in biventricular hypertrophy and diastolic dysfunction [64]. Poor right ventricular systolic function can lead to functional right ventricular outflow tract obstruction in up to 10% of recipient twins, which may progress to severe pulmonic stenosis and a poor prognosis [64]. In contrast, recipient twins with normal cardiac function have improved survival [65]. Therefore, in addition to excluding structural heart defects in monochorionic twins, fetal echocardiography with a detailed functional assessment may be useful in identifying cases of twin-twin transfusion syndrome that would benefit from fetoscopic laser therapy and in evaluating the response to treatment.