Are Identical Twins the Same Height? 3 Determining Factors

Identical twins, also known as monozygotic twins, share a striking similarity in appearance. However, upon closer examination, to what extent do they truly resemble each other?

Are identical twins the same height?

While identical twins can be the same height, that is not usually the case. One twin is generally taller and heavier than the other twin. Both nature and nurture play a role in what happens to each twin as soon as the ovum has divided into two. 

Imagine being a medical student in a busy Los Angeles hospital in 1984. You witness the birth of a baby and are told to deliver the placenta. A head starts to appear, and only then do you realize this is a case of undiagnosed twins. 

You deliver the second baby and then the placenta. Without ever seeing the twins again, you can surmise that these were identical twins because of one placenta and the twin you delivered will be shorter than the first born twin. 

Height Differences in Identical Twins

Differences and similarities of height in identical twins and the causes are being explored by scientists around the world. Twin studies started almost 150 years ago, and we still have much to learn. 

Are Identical Twins Always the Same Height?

Identical twins are not always the same height. Gene suppression and gene mutation can both affect how tall a twin will grow to be. 

What Is the Average Height Difference Between Twins?

According to Nancy Segal, Ph. D., the average height difference between a set of twins is 2 inches. 

What Causes Height Differences in Identical Twins?

There is no single cause that determines the height of twins. Scientists are still studying and learning about monozygotic twins. For years, the nature vs. nurture debate was a hot topic. 

By now, we have come to realize that it is both forces that play a role in how people develop both physically and emotionally. Nature pertains to genes, biology, and what can be inherited. Nurture pertains to environment and experiences. 

The question is no longer about nature vs. nurture but rather how nature and nurture influence each other. The height of a twin can be influenced by many factors, and more information is being discovered every year.


A person’s height is largely determined by DNA. A child’s potential height will be affected by approximately 80 percent of inherited DNA variants. 


Biological factors, such as growth hormones, thyroid hormones, and sex hormones, are also contributing components 


Where and how a twin grows up will affect their height potential. This actually begins in the womb. More specifically, it is the non-shared environments that affect gene expression in identical twins causing their differences rather than their likenesses. 

Examples of non-shared environments are being in different classrooms at school, experiencing a trauma or a happy event, or being involved in a hobby. If each twin has their own set of experiences, it will have an effect over time. Some identical twins share a placenta, but others may have their own placenta. 

Most twins start out having their own room in the womb, so no wonder they have differences even before their birth. Each child has their own umbilical cord. If one twin has a cord that is shorter than the other twin’s cord, it is believed that the twin with the shorter cord will have more nutrients and oxygen

Which Twin Is Usually Taller?

First-born twins are usually taller. There have only been a few studies on why this occurs. So far, scientists see a strong correlation between having an optimal womb position and a higher birth weight. Overall, the first-born twin will be taller and weigh more. 

Do Identical Twins Grow at the Same Rate?

It is perfectly normal for twins to grow at their own rate, both before and after birth. These kiddos have been labeled as “identical,” but each twin is a unique individual. Epigenetics also play a key role in the growth of twins. When twins make food, social, exercise, drug, housing, medical, and traveling choices, it all affects their genetic makeup. 

Can Identical Twins Have Different Body Types?

Twins usually have similar body types unless one actively chooses to make a difference. A twin who chooses a more active lifestyle will have a lower BMI, more muscle tone, and a higher endurance capacity. 

Can Identical Twins Look Different?

Monozygotic twins look similar because they share over 99.9% of their DNA. Do not underestimate the less than one-tenth of a percent when it comes to differences in identical twins. Mutations start to happen early on, resulting in many changes in the unborn twins. 

An extreme example would be of Adam and Neil Pearson, who both have a rare genetic disorder called neurofibromatosis. They have been affected in different ways. The most obvious is that these identical twins do not look alike at all.  

Related Questions:

Do Twins Have Growth Spurts at the Same Time?

Twins may have growth spurts at around the same time. Typical growth spurts for any child can be expected at about ages 3 weeks, 6 weeks, 3 months, and 6 months old. 

Do Twins Have Delayed Puberty?

Twins go through puberty much like singletons do — whenever their biological clock goes off so to speak. One twin’s bio clock might be ringing loud and clear while the other twin’s bio clock has hit the snooze button a few times. 

It is important to normalize the timing of your twins pubescent onset, especially if one is lagging behind the other and their peers. 


As with many things concerning identical twins, their heights might be close but not exactly the same. Anything can affect the growing twins from who got the bigger placenta to who got more sleep. Both nature and nurture affect the growth of twins.