Why Does an Embryo Split into Twins?

During IVF, the blastocoel may collapse on itself. While this typically destroys the embryo, sometimes the embryo survives, causing the inner cell mass to split into two. The two inner cell masses lead to the development of twins.

When would an embryo split into twins?

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). These are known as "monozygotic" twins (or triplets).

What causes fragmentation in embryos?

Embryo fragmentation is associated with a range of factors, including inadequate culture conditions, poor quality of the ovum and spermatozoon [1], increased maternal age [2,3], chromosomal abnormalities [4], abnormal cell cycle [5], apoptosis [6], and oxidative stress in embryos [7].