Multiple Births: Twins, Triplets, and Quadruplets Explained

Understanding Multiple Births

Multiple births occur when more than one fetus develops during a single pregnancy. The most common types are twins, triplets, and quadruplets, each with distinct biological origins.

Twins

Fraternal (dizygotic) twins result from two separate eggs fertilized by two separate sperm cells. They share about 50% of their DNA, just like regular siblings, and can be of the same or different sexes.

Identical (monozygotic) twins develop from a single fertilized egg that splits into two embryos. They share 100% of their DNA and are always the same sex.

Triplets

Triplets can arise in several ways:

• Trichorionic triamniotic: Three separate eggs fertilized by three separate sperm (most common).
• Dichorionic triamniotic: Two eggs fertilized, one splits into identical twins, plus a third fraternal sibling.
• Monochorionic triamniotic: A single egg splits into three identical embryos (rare).

Quadruplets

Quadruplets follow similar patterns but with four embryos. They can be all fraternal (four eggs), a mix of identical and fraternal, or rarely, all identical from one egg splitting multiple times.

Higher-order multiples (quintuplets, etc.) are increasingly rare and often result from fertility treatments.