What type of twinning occurs when cleavage happens between days 0 to 3 of fertilization?

The type of twinning that occurs when cleavage happens between days 0 to 3 of fertilization is known as di/di twins, or dichorionic-diamniotic twins. During this early cleavage stage, the zygote divides into two separate embryos before the formation of a single placenta or amniotic sac. Each twin develops independently, surrounded by its own chorion (outer membrane) and amnion (inner membrane), which is why they are classified as dichorionic and diamniotic.

This type of twinning is often associated with fraternal twins (dizygotic), where two separate eggs are fertilized by two separate sperm and develop independently. In the case of identical twins (monozygotic), if division occurs later than day 3 but prior to day 8, the twins may be mono/di, sharing the same placenta but having separate amniotic sacs. If division occurs even later, after day 8, the twins can end up being mono/mono, sharing both the placenta and the amniotic sac, which can lead to complications. Conjoined twins result from an incomplete division of the embryo after day 12. Hence, the characteristics of di/di twins occurring from