Twins have the unique experience of growing in the same womb, which limits the amount of space they have for development compared to single babies. This raises the question of how this limitation affects their growth in comparison to single babies.
Are twins generally shorter? Twins do tend to be shorter than their singleton peers. While the reasons for this vary, the difference in height usually exists in childhood but may disappear by adulthood. While some studies show a slight difference in adult twin heights compared to singletons, data is limited in scope.
Understanding everything that affects the height of twins means taking an in-depth look at what we know so far. A variety of factors will determine how tall or short your twins end up being.
Twin Height – What To Know
Doctors will monitor the growth of your twins in the womb to make sure they are doing well and growing at an appropriate rate. Their height and weight will be tracked closely.
Average Twin Height at Birth
Twins do tend to be shorter at birth than single babies, though no definitive study has shown averages for height since most focus on weight.
Twin Height & Growth During Childhood
Twins are generally shorter than their peers during childhood. This could be because of premature birth, intrauterine growth restriction, or other factors that impact growth.
Twins may be the same height during childhood, but they might not. If one twin was not getting the same amount of nutrients from the placenta, then he may be shorter than his sibling.
Twin Height at Adulthood
Fraternal twins can be the same or different heights in adulthood. The fact that they do not share identical genes means it’s anyone’s guess as to how similar they will be.
As far as how they rate compared to singletons, not much research has been done.
Identical twins are usually shorter than singletons, even as adults. They will likely be close to the same height as adults since they share the same genes, though environmental factors and health can impact growth outside of the womb.
Do Twins Grow at the Same Rate?
Many people assume that everything, including growth rate, is the same with twins. However, this is not the case.
Growth in the Womb
In the womb, twins do not always grow at the same rate. Identical twins often share a placenta, and this makes tracking growth even more important when babies are in the womb.
If blood supply from the placenta is not equal for both twins, they won’t grow at the same rate.
While some differences are considered normal, others are cause for concern. Twin-to-twin transfusion syndrome occurs when growth is majorly affected, and it may require an early delivery or other intervention.
Compared to Each Other
For identical twins, heights often are very similar because of how much is impacted by genetics. Fraternal twins share the same amount of genes as non-twin siblings, so their heights could vary as much as any other siblings.
Compared to Others
Though research is limited, twins tend to be slightly shorter than their singleton counterparts. The height differences persist into adulthood, even if the differences are small.
Is One Twin Usually Bigger Than the Other?
Often one twin is bigger than the other, even if only slightly. The first-born twin is often the bigger one at birth.
Which Twin Is Usually Taller?
The first-born twin tends to be taller than the second-born twin, at least in childhood.
Fraternal Twins Growing at Different Rates
Fraternal twins can grow at different rates in the womb. Though it’s not common, fraternal twins can share a placenta, which means one twin may be getting more nutrients than the other.
Fraternal twins with their own placentas don’t usually have as many growth issues and will likely grow at similar rates. However, they also only share half of the same genes, so one may grow at a different rate simply due to genetics.
Can Identical Twins Be Different Heights?
Yes, identical twins can be different heights. Though they share the same genes, height is not only controlled by genes, as research has shown.
Using identical twins in the studies has helped scientists see that height is probably affected by DNA and other factors since not all identical twins are the same height.
What Determines Height? 5 Influencing Factors
There are certain factors that affect height, and each of these contributes to a certain extent.
1. Genetic Makeup
Genetics is the main reason people end up being the height they are. It is said that genetics gets credit for about 80 percent of a person’s height.
For identical twins who share the same genes, this means they will likely be the same height or very close.
2. Nutrition
Nutrition is important as your children develop in the womb and when they are growing outside of the womb. Make sure your kids eat healthy foods and that they get enough of them.
When babies are in utero, doctors will monitor their growth, especially when you are having twins. They will make sure nutrients are being divided properly and that both babies are getting what they need.
3. Hormones
Growth hormones, sex hormones, and thyroid hormones all have a role to play when it comes to height.
If your child has problems with their thyroid or issues that impact growth hormones, they may grow at a slower rate or be shorter than other children.
4. Environment
If your children grow up in a house where they don’t get enough sleep, food, or physical activity, height can be adversely impacted. The right environment for mental and physical growth makes a difference in everything, including height.
5. Medical Issues
There are medical issues that can slow down a child’s growth or keep it from progressing altogether. Treatments may help a child recover, but that doesn’t mean they will ever grow at the same rate as children without the same medical issues.
Final Thoughts
The height of twins depends on a lot of different things, and it can vary based on the type of twins you have. As long as they are healthy and happy, try not to worry too much about their height.
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.