Most common twin after assisted reproduction is

(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.