Accuracy of Sonographic Chorionicity Classification in Twin Gestations

The rate of twin gestations continues to rise, accounting for approximately 33 of 1000 births in 2009.1 Compared with dichorionic twins, monochorionic twins have inherently different complication rates, including fetal loss, fetal anomalies, intrauterine growth restriction, and prematurity.2–7 Monochorionic twins are also at risk for twin-twin transfusion syndrome (TTTS) and twin anemia polycythemia sequence. Therefore, recommendations regarding antepartum surveillance and delivery timing differ by chorionicity, and accurate determination of chorionicity is vital when managing twin gestations. The sonographic accuracy of chorionicity classification has been previously studied, and reported accuracy rates differ by gestational age at the time of assessment, center experience, and number of sonographic variables used.8–15 However, prior reports have been limited by relatively small numbers. In addition, these studies have not evaluated factors that may potentially limit sonographic accuracy, such as maternal body mass index (BMI), underlying maternal medical disorders, and prior cesarean delivery. The objective of this study was to evaluate the sonographic accuracy of chorionicity classification in multiple gestations using a large multicenter cohort. In addition, we aimed to study whether maternal, obstetric, and sonographic factors were associated with accuracy.