Q. I understand how twins are made, but what about triplets? What’s the deal there?
Triplets may occur in one of 3 ways:
- 3 different eggs are fertilized by 3 different sperm, producing 3 fraternal triplets
- 1 egg is fertilized and then splits twice to form three zygotes, which would create identical triplets
- 2 eggs are fertilized, with one egg splitting to create twins and the other egg remaining as a single zygote, which would mean the triplets are a set of identical twins and a fraternal sibling
The first scenario is rare naturally, because women don’t usually produce 3 or more eggs when ovulating. However, with fertility treatments more common than in the past, women taking fertility drugs are producing multiple eggs each month, increasing the odds of having fraternal triplets.
The second scenario is also rare — it is extremely uncommon to have identical triplets.
The third scenario is the most common way triplets are produced — two eggs are fertilized, but one splits to form a set of twins, with three children being born overall.