Zygotic splitting occurs between days two and six when the zygote divides, usually into two, and each zygote then goes on to develop into an embryo, leading to identical twins (or triplets if it divides into three).

What causes zygotic splitting?

However, at present, the cause of zygotic splitting remains unknown. The patient's genetic predisposition, including PCOS itself, the effects of drugs administered before oocytes collection, and the effects of in vitro maturation culture may also be related to zygotic splitting [29].

At what week does an embryo split into twins?

Splitting of the embryo may occur at any time during the first 2 weeks after fertilization, resulting in several forms of monozygotic twins.