Pregnancy

Types of Multiples

 

There are two types of twins: monozygotic (identical) and dizygotic (fraternal).

Identical twins

Identical twins result from a single fertilized 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 color.

Fraternal twins

Fraternal twins come from two eggs that are fertilized by two separate sperm and are no more alike than other siblings born to the same parents. 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, race, and number of prior pregnancies.

"Supertwins"

"Supertwins" is a common term for triplets and other higher-order multiple births, such as quadruplets or quintuplets. These babies can be identical, fraternal, or a combination of both. But higher-order births are rare; triplets occur in approximately 1 in 7,000 to 8,000 births, whereas quintuplets are likely to be born only once in 47 million births.