When does twinning happen (embryo splits)?
A very common question is when twinning occurs or at what point the embryo split occurs in identical twins.
Splitting of the embryo can occur in a few stages of development. Twinning can happen anywhere between the third to the thirteenth day after conception.
Three-day gap
Some identical twins are produced when an embryo develops from a single fertilized cell to a zygote, as the name “identical twins” suggests.
The zygote breaks into two cells, usually on day three of a singleton (one baby) pregnancy, but the cells are still joined together. However, in twinning, those two cells completely divide into two different entities rather than remaining united.
Twins created from a two-cell split are more likely to have a high level of genetic variation or mutations between them. The possibility of mutation increases with the age of the split.