Do Triplets Always Look Alike?

Understanding Zygosity in Multiples

When someone hears you’re having multiples, one of the first questions is usually: “Are they identical?” It’s a fair question, but the answer is rarely simple. Triplets don’t always look alike, and the science behind it is fascinating.

In this blog, we’ll explore what zygosity means, how it affects whether multiples look alike, and the different ways triplets can (and do) arrive in the world.

What is zygosity?

Zygosity refers to the genetic similarity between siblings born at the same time. It describes how many eggs and sperm were involved in creating a set of multiples. There are three main types:

• Monozygotic (Identical) – One egg + one sperm = one embryo that splits

• Dizygotic (Fraternal) – Two eggs + two sperm = two genetically unique embryos

• Trizygotic – Three eggs + three sperm = three genetically unique babies (most common in spontaneous triplets)

How can triplets form?

Here’s where things get interesting: triplets can be identical, fraternal, or a mix of both.

Identical Triplets (Monozygotic)

• Very rare (about 1 in 100,000 births)

• One fertilised egg splits into three embryos

• All three babies share the exact same DNA

• Usually look very similar (but not always exactly the same, environment and birth order matter too!)

Fraternal Triplets (Trizygotic)

• Three separate eggs are fertilised by three separate sperm

• Babies are no more alike than regular siblings

• They may all be the same sex or a mix of boys and girls

• Can look quite different from each other

A Combination (Mixed Zygosity)

• Example: One egg splits into identical twins, and another egg is fertilised separately

• Result: Two identical babies + one fraternal sibling

• This is more common than most people realise!

Can You Tell Just by Looking?

Not always! While identical triplets may look strikingly alike, it’s not a guarantee. Some reasons why:

• Position in the womb can affect head shape and size

• Slight genetic mutations can occur during cell division

• Environment, feeding, and early experiences can shape appearance

And just like any siblings, fraternal triplets can still share some similar features!

How can I find out my triplets’ zygosity?

It’s not always clear at birth, especially if all babies are the same sex. Here’s how you can find out:

• Placenta and sac information at birth (it may be possible to tell based on how many placentas or sacs were present)

• DNA testing – The most accurate method, especially if you want certainty

• Physical resemblance – Sometimes helpful, but not reliable on its own

Some families choose to test just for fun or curiosity. Others want to understand medical risks, as identical siblings share more health traits and genetic risks.

So, do triplets always look alike?

Nope, and that’s part of the magic! Your trio might be identical, fraternal, or a fascinating mix, and each one will grow into their own personality, quirks, and style.

Whether they’re mirror images or totally unique, one thing’s for sure: your hands are full, and your heart is fuller.