قسمتی از اسلایدها Etiology : More commonly fertilization of two ova with tow sperm double ovum or fratermal or dizygotic twins About tow third. A bout one third as often nOne fertilized ovum divided into two similar structures, into a separate individual that we call it a single ovum – monozygotic or Identical twins nEither or both process may be involved in the formation of high number of fetuses . &n ...