The interest of twin chorionocity and zygosity diagnosis is unquestioned. Indeed, in many medical situations, the knowledge of zygosity is an important fact for management of twins. Prenatal echographia is not a perfect tool to characterize chorionicity, and so postnatal examination of the placenta is always necessary. But macroscopic examination is also not relevant, and competent midwives can make many mistakes. Considering that biological postnatal diagnosis of twin zygosity is difficult and costly, we believe that microscopic chorionicity confirmation is required for identical twins.