<prompt> Least common type of twins-Diamniotic-dichorionic twinsDiamniotic -monochorionic twinsMonoamniotic-monochorionic twinsConjoined twins  <response>: 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 DD 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 DM 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 MM 3:- if the division takes place after 8th day of fertilization when amniotic cavity has already formed. 4 Conjoined twin or Siamese twin 