Over the past 30 years there has been an increase in the number of multiple births globally. Since 1980, the number of twin births has increased by 70% in the USA and the number of births involving three or more babies has quadrupled.
The two main reasons for this increase are that women are having babies later, and more women are having fertility treatment, such as in vitro fertilisation (IVF).
The biggest increases in multiple births are among women aged 30 and older. Older maternal age accounts for about one-third of the rise, and two-thirds is due to the increased use of fertility treatments.
Other factors that contribute to the development of a multiple pregnancy are heredity: a history of multiple births on a woman’s side of the family increases her chances of having a multiple pregnancy; and race: women of African descent are the most likely to have multiple pregnancies
Types of Multiple Births
Identical twins result from a single fertilised egg dividing into separate halves and continuing to develop into two separate but identical babies. These twins are genetically identical, with the same chromosomes and similar physical characteristics. They’re the same sex and have the same blood type, hair, and eye colour.
Fraternal twins come from two eggs that are fertilised by two separate sperm. They may or may not be the same sex. This type of twins is much more common, and only this type is affected by heredity, maternal age and race.
‘Supertwins’ refers to the rarity of triplets, quadruplets or quintuplets. These babies can be identical, fraternal, or a combination of both. The odds of having triplets is around one in 7 000 to 8 000 births, while quintuplets are likely only once in 47 million births.