Twin Pregnancy at 58: Understanding the Science, Risks, and the Rare Possibility of Later-Life Births

The Two Main Types of Twins
Twin pregnancies generally fall into two categories:

Fraternal Twins (Dizygotic)
These occur when two separate eggs are released during ovulation and fertilized by two different sperm cells. Fraternal twins can be the same or different sexes and share about half of their DNA, similar to regular siblings. This type is often influenced by genetics and hormonal patterns.

Identical Twins (Monozygotic)
These happen when a single fertilized egg splits into two embryos. Identical twins share nearly identical genetic material and are always the same sex. This process is generally random and not strongly influenced by heredity.

Both types result in multiple births, but they form through very different biological processes.

Genetic Influence on Twin Pregnancies
Genetics can play a role, particularly in fraternal twins. Some women inherit a tendency for hyperovulation, which means the ovaries release more than one egg during a cycle.

If a woman has close relatives—such as a mother or grandmother—who had fraternal twins, her chances may be slightly higher. However, this does not apply to identical twins, which occur by chance.