Facts about Multiples

New Zealand Statistics 2015

Statistics New Zealand have recently released birth figures for the 2015 year. In 2015 there were 828 sets of twins born and 14 sets of triplets (these figures include stillbirths). This is up slightly from 2014 (808 sets twins and 11 sets of triplets) but total births were also higher. Multiple births accounted for 1.39% of all births in 2015 compared to 1.44% in 2014. There hasnít been a set of quads born in New Zealand since 1998! See the Fact Sheet for more information.

Other New Zealand Statistics

Twins make up about 2% of all pregnancies in New Zealand, 75% of these will be fraternal and 25% identical.

One in 80 births produces non-identical twins and women who have had non-identical twins are four times more likely to conceive twins again. Daughters of women who have had non-identical twins are 1.8 times more likely to have non-identical twins themselves. Sisters of women who have had non-identical twins are 2.6 times more likely to have non-identical twins. Non-identical twins are directly inherited through the mother, either from her mother or father.

It has now been established that in some cases identical twins may run in families. However, in most cases they just happen. Identical twins are always the same sex.

Twins do not "skip" generations, but can often be born in every generation.

Triplets and quadruplets can also be inherited. They can be a combination of identical and fraternal babies.

The main reason for the increase in the incidence of multiple births is the shift to later childbearing. Another contributing factor is the use of fertility enhancing treatments. Source: NZ Statistics

Siamese Twins

Siamese, or conjoined, twins are extremely rare, occurring in as few as one in every 200,000 births. The twins originate from a single fertilised egg, so they are always identical and of the same sex.

The developing embryo starts to split into identical twins within the first two weeks after conception.

However, the process stops before it is complete, leaving a partially separated egg which develops into a conjoined foetus.

The birth of two connected babies can be extremely traumatic and approximately 40-60% of these births are delivered stillborn with 35% surviving just one day.

The overall survival rate of conjoined twins is somewhere between 5% and 25%.

Historical records over the past 500 years detail about 600 surviving sets of conjoined twins with more than 70% of those surviving pairs resulting in female twins.

If they have separate sets of organs, chances for surgery and survival are greater than if they share the same organs.

Conjoined twins are generally classified three ways:

Over the years, survival rates have improved as a result of more accurate imaging studies and better anaesthetic and operative techniques.

The term siamese twins was coined as a reference to Eng and Chang Bunker, who achieved international fame following their birth in what was then Siam in 1811.

They were exhibited in circus side shows around the world before settling in the United States and marrying two sisters. They lived 63 years, with Chang fathering 12 children and Eng 10.

Australian Twin Registry

Facts and figures about twins from the Australian Twin Registry.