<prompt> Most common twin after assisted reproduction isAcardiac twinMonozygotic twinDizygotic twinConjoined twin  <response>: C Dizygotic twin?Prevalence of Dizygotic twins is related to:Race: The frequency is highest amongst Negroes, lowest amongst Mongols intermediate amongst Caucasians.Hereditary: There is hereditary predisposition likely to be more transmitted through the female maternal side.Advancing age of the mother: Increased incidence of twinning is observed with the advancing age of the mother, the maximum being between the age of 30-35 years. The incidence of twins is markedly reduced thereafter.Influence of parity: The incidence is increased with increasing parity specially from 5th gravida onwards.Iatrogenic: Drugs used for induction of ovulation may produce multiple fetuses to the extent of 20-40 following gonadotrophin therapy, although to a lesser extent 5-6 following clomiphene citrate.Dizygotic twins:There are two placentae, either completely separated or more commonly fused at the margin appearing to be one 9 out of 10. There is no anastomosis between the two fetal vessels.Each fetus is surrounded by a separate amnion chorion.As such, intervening membranes consist of 4 layers - amnion, chorion, chorion amnion. In fact in early pregnancy the decidua capsularis of each sac may be identified under the microscope in between the chorionic layers. Other Options?Monozygotic twins:The placenta is single. There is varying degree of free anastomosis between the two fetal vessels.Each fetus is surrounded by a separate amniotic sac with the chorionic layer common to both Diamniotic-monochorionic.As such the intervening membranes consist of two layers of amnion only. However, on rare occasions, the uniovular twins may be diamniotic-dichorionic or mono-amniotic-monochorionic.?Fetus acardiacus:It occurs only in monozygotic twins. Part of one fetus remains amorphous becomes parasitic without a heart. 