Least common type of twins-

Ans. is d i.e., Conjoined twins Dizygotic twins 180%) o Result from fertilization of two ova, most likely ruptured from two distinct Graffian follicles usually from same or one from each ovary, bye two sperms during a single ovarian cycle. Monozygotic twins (20%) o Twinning may occur at different periods after fertilization. On rare occasion following possibilities may occur Diamniotic-dichorionic or D/D {30%):- if the division takes place within 72 hrs after the fertilization (prior to morula stage) resulting embryo will have two separate placenta, chorions and amnions. Diamniotic-monochorionic or D/M (66%):- if the division takes place between 4th & 8th day after the formation of inner cell mass when chorion has already developed. Monochorionic-monoamniotic or M/M (3%):- if the division takes place after 8th day of fertilization when amniotic cavity has already formed. 4) Conjoined twin or Siamese twin (<f %):- if the division takes place after 2 weeks of development of embryonic disc.