Like twins, triplets and other higher-order multiples can be categorised by their zygosity. While many people are familiar with the terms “identical” and “fraternal” in describing multiples and use these terms to define whether twins or triplets look similar, what they are really referring to is how the multiples form.

Most triplets are trizygotic, meaning that each individual forms from a separate zygote, or egg/sperm combination. They are commonly described as “fraternal” multiples and share the same genetic similarities as any siblings. However, it is not uncommon for triplets to be dizygotic, which occurs when two eggs are fertilized by sperm, and one of the fertilized eggs splits into two. Essentially, two of the triplets are monozygotic (identical) twins, sharing the same general DNA characteristics, while the third multiple was produced by a different egg/sperm combination and has a unique genetic makeup, distinct from that of the other two triplets.

Naturally with higher order multiples the possible permutations increase…

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