Last reviewed 04/2022

Twins occur in 1 in 105 births in the UK.

Twins may be polyzygous (binovular) (these are twins that develop from two separate ova that were fertilized at the same time) or monozygous (uniovular) twins which develop from the same ova.

Polyzygous are termed non-identical twins. These twins never share the same amnion, chorion or placenta. There may be, however, fusion of separate placentae.

The incidence of binovular twins is three times that of uniovular twins.