New Zealand Multiple Birth Association

About Multiple Pregnancy

Twins make up about 2% of all pregnancies in New Zealand, 75% of these will be fraternal and 25% identical. Triplet and higher order pregnancies can be fraternal or identical, or a mixture of both.

There are two main types of twins, and twinning occurs in one of two ways:

  • Fraternal twins (dichorionic) occur when two eggs are released by the mother, at about the same time, and are fertilised by two different sperm
  • Identical twins (monochorionic) are the result of a single fertilised egg dividing in two, resulting in two babies who share about 90% of their genes.


'Chorionic' relates to how the amniotic membranes are set up, and is diagnosed by ultrasound.

For more information on twin types, click here.

For an article about the latest research on twin types, click here.


 Types of Twins

This diagram shows the different ways that the amniotic membranes and placentas can occur with identical twins.