Histopathological examination of the placenta in twin pregnancies.

Twin placentas are frequently received in pathology laboratories for evaluation of chorionicity and because twin pregnancies have higher rates of pregnancy complications. In addition to pathologies common in singleton pregnancies, twin pregnancies have increased frequencies of complications such as preterm birth and velamentous cord insertions and also are affected by complications unique to multiple pregnancies that are mediated by vascular connections between the placental territories of certain types of twins. This article aims to provide an approach to examination of the twin placenta for practicing pathologists or those interested in placental pathology while outlining the key characteristics of twin complications as seen in the placenta.