Upon discovering the news of having twins, it is natural to assume that they will share a strong physical resemblance. This was my initial thought upon receiving confirmation of my own twin pregnancy.
However, not all twins look alike, and some twins look so different that it’s hard for anyone to even tell they shared a womb.
Fraternal twins might look like siblings, but they won’t have identical features because they came from different eggs. It’s also possible for twins to have different fathers, but this is rare. Even identical twins can look different due to genetic mutations and environmental factors.
If you understand how twins are conceived, it’s easier to understand why some look identical and others don’t look alike at all.
Why Not All Twins Look Alike
Twins are two different people who share the same womb, so it’s normal for them to have some physical differences.
Depending on the type of twins and the parentage of the twins, your twins may look a lot alike or not alike at all.
Identical vs. Fraternal Twins
Identical twins are conceived when one fertilized egg splits in two.
Identical twins share more genetic material than fraternal twins, and they often look alike. Identical twins are also the same gender.
Fraternal twins occur when two separate eggs are fertilized by two separate sperm.
These twins share a womb, but they are only as genetically similar just as ordinary siblings. They can also be different genders, and they may not look alike.
Twins With Different Fathers
Twins can have different fathers, though this only occurs with fraternal twins.
If a woman releases two eggs instead of one and each egg is fertilized by sperm from a different man, she can end up with twins who have different fathers.
This is called heteropaternal superfecundation. It’s not common, but it can occur.
These twins will likely not look much alike because their mother is the only parent they will have in common.
Biracial Twins
There is a set of fraternal twins who look nothing alike because one is so fair and the other is not.
They were born to a biracial couple, and they don’t even look like they are related. However, they are biracial, fraternal twins.
There was a more recent case of identical biracial twins being born with different color skin and eyes. Though they share most of their genes, they do not look like twins.
Even Identical Twins Have Slight Differences
I have identical twins, and while they look very much alike, there are still differences (birthmarks, for example). As they have aged, it’s gotten easier to tell them apart.
Their faces have slightly different shapes, their birthmarks are in different areas, and they carry themselves differently when they walk.
What To Know About Fraternal Twins
Fraternal twins are more common than identical twins, and they also may not be the same gender.
Since two eggs are fertilized by two different sperm when fraternal twins are conceived, they may not look any more similar than non-twin siblings.
You are more likely to have fraternal twins with fertility treatment than identical twins, and fraternal twin pregnancies tend to be lower risk than identical twin pregnancies.
You could also have fraternal twins who look very much alike, and you may constantly get asked if they are identical.
Can Identical Twins Look Completely Different?
Identical twins can look completely different. However, it’s more common for them to look very similar due to how they are conceived.
One fertilized egg splitting means identical twins share almost all of their genes.
Though slight mutations can change the DNA slightly, they still share more genetic material than any other type of siblings. They will likely look either identical or very close to it.
In a case such as that of biracial identical twins, a rare occurrence that was first noted about a decade ago, identical twins could look different. However, the chances of this occurring are extremely low.
Rare Types of Twins
There are subtypes of twins that fit within the categories of identical and fraternal. These are rare, but they do exist and can make studying twins even more interesting.
Conjoined Twins
Conjoined twins, a type of identical twinning, occur when an egg does not split all the way before implanting.
Many conjoined twins die before birth, and those who do make it often undergo life-threatening surgery to be separated.
Superfetation
When you’re pregnant, you’re not supposed to ovulate, but it has been known to happen in very rare cases.
If a woman ovulates when she is already pregnant, she could get pregnant again.
These siblings would technically be twins since they share the womb, but they may not even be ready to be born at the same time.
Heteropaternal Superfetation
Though uncommon, a woman who releases more than one egg in a cycle can get pregnant with twins from different fathers. This is not common, but it is possible.
Mirror-Image Twins
Some identical twins can stand face-to-face and have the same features on opposite sides of their bodies, like a mirror image.
This is thought to occur when an egg splits more than a week after fertilization. Mirror-image twins are a type of identical twins.
Related Questions:
Why Do Identical Twins Look Different as They Get Older?
As my identical twins get older, they look different. Though still obviously twins, their lifestyle choices affect their appearance.
How a person chooses to eat, move, and take care of their body affects appearance.
It’s also possible for twins to change as they move to different locations and get exposure to different environments. This is more common when they are older.
Can Identical Twins Look Different at Birth?
Yes, identical twins can look different at birth. My twins had twin anemia polycythemia sequence (TAPS), so one was very red while the other was pale due to the condition.
Some twins have startling weight differences when they exit the womb due to twin-to-twin transfusion syndrome (TTTS). It’s also possible for twins to just look different, even if they are identical.
Final Thoughts
No matter what your twins look like, they will likely have a unique bond since they shared a womb.
Whether or not they are identical, you’ll love them equally and wonder how you ever lived without them!
Kristy is the mother of four, including identical twins. With a background in education and research, she is constantly learning more about parenting and raising multiples. When she has spare time, she enjoys hiking into the woods with a great book to take a break.