If zygote divides between 4-8 days post feilization, following twinning occurs
The outcome of the monozygotic twinning process depends on when division occurs.At 0 to 4 days postfeilization, an early conceptus may divide into two. Division at this early stage creates two chorions and two amnions (dichorionic, diamniotic). Placentas may be separate or fused. Division between 4 to 8 days leads to formation of a blastocyst with two separate embryoblast (inner cell masses). Each embryoblast will form its own amnion within a shared chorion (monochorionic, diamniotic).Between 8 and 12 days, the amnion and amnionic cavity from above the germinal disc. Embryonic division leads to two embryos with a shared amnion and shared chorion (monochorionic, monoamniotic).Conjoined twins result if twinning is initiated laterReference: William's Obstetrics; 25th edition; Chapter 45; Multifetal pregnancy
Dichorionic Diamniotic
Monochorionic Diamniotic
Monochorionic Monoamniotic
Conjoined twins
General obstetrics