An ultrasound performed on a women, shows twin pregnancy. Which of the following is a feature of dizygotic twins?

In Dizygotic twins, each twin has separate amnion and chorion and the intervening membrane consists of 4 layers amnion, chorion, chorion and amnion. They have two placentae either completely separated or more commonly fused at the margin appearing to be one. There is no anastomosis between two fetal vessels. In monozygotic twins: There is only a single placenta, there is varying degree of anastomosis between two foetal vessels. Each fetus is surrounded by a separate amniotic sac with the chorion layer common to both (diamniotic monochorionic). Intervening membrane consist of two layers of amnion only. Ref: Textbook of Obstetrics By DC Dutta, 6th edn, page 203