Conjoined livers are very common and there is an increased incidence of congenital heart disease not obviously linked to the conjoined abdomen. Ileopagus - connected at the iliac bone. When the twins are extensively connected then the duplicated part is named. For example, dicephalus refers to two heads with one body. If the split occurs before this time the monozygotic twins will implant as separate blastocysts each with their own chorion and amnion.
All dichorionic twins are diamniotic.
Eight days after fertilization the amnion differentiates. If the split occurs between the 4th and 8th days, then the twins will share the same chorion but have separate amnions. If a split occurs after the 8th day and before the 13th day, then twins will share the same chorion and amnion. The embryonic disk starts to differentiate on the 13th day. If the split occurs after day 13, then the twins will share body parts in addition to sharing their chorion and amnion.