Male-female, the most common pairing

Twins are two offsprings produced by the same pregnancy. Twins can be either identical (or monozygotic), meaning that they develop from a single egg that splits and forms two embryos; or fraternal twins (dizygotic), meaning that each twin develops from a separate egg and each egg is fertilised by its own sperm cell.

Dizygotic twins, also referred to as “non-identical twins”, or “dissimilar twins”, are the most common type of twins.

Twins can be female–female (sororal twins), male–male or male–female. The latter is the most common pairing. Half of all fraternal (dizygotic) twins are male-female.