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Twins – and more

identical; triplets; sperm; egg; uterus; pregnant; baby; twins; multiple;


Chances of being a twin

twinsThe chances of being born a twin are about 3 in 100. The chances of being born an identical twin are about 1 in 250. When more than one baby is born (twins or more), this is called a multiple (say mul-ti-pul) birth.

A few years ago more multiple births were happening because some women who were having problems getting pregnant were able to have a special treatment called fertility treatment. This sometimes led to more than one baby. Nowadays the treatment has changed so that usually only one baby is born.

Three babies together are called triplets, 4 are called quadruplets (quads), and 5 are quintuplets (quins).

Identical twins

Identical twins happen when a single sperm from the father fertilizes a single egg from the mother.

Soon afterwards this fertilized egg divides into two and starts forming two babies.

  • identical twinsThey will have identical genes.
  • They are the same sex.
  • Some identical twins will share the same placenta (where they get the nutrients needed to grow) and the same sac, a kind of bag for the baby inside the mother's womb or uterus.
  • Some identical twins will have their own placenta and sac inside the mother's uterus.
  • Some identical twins may be different sizes when they are born but they usually are about the same size when they are 6 months old.
  • Identical twins may not start off looking identical but they grow more alike as they get older and it can be hard for others to work out who's who.

Non-identical twins

fraternal twinsNon-identical twins are sometimes called fraternal twins. Fra-ter-nal means brother.

  • Fraternal twins can be both boys, both girls, or one of each.   
  • They are formed when 2 sperm fertilise
    2 eggs.
  • Each has its own place in the uterus.
  • Each has a placenta and sac.
  • These twins often look very alike at birth but may grow less alike as they get older, just like other kids in the family.

'Siamese' twins

There are also, in very, very rare cases, conjoined or 'Siamese' twins. These are babies who are joined together and may share some parts of their bodies. Their heads may be joined together, or a different body part is joined.

These twins come from the same egg but it hasn't divided properly. They are always the same sex.

identical twins

Being a twin

Having another person who is the same age as you can be really great! You always have someone the same age to play with. But that doesn't mean that you are always going to be the best of friends. Just like other siblings you may have some good times and some bad times.

identical twinsIf you are identical you might have a lot of fun confusing others who can't tell you apart but it can be annoying to be called your twin's name all the time. People might assume because you are identical to look at then you are identical in other ways. It can be hard to be an individual!

It can be annoying if one of you is really good at something and the other one isn't. What if you are not really good at sport and the other one is? You can come in for a lot of comments like, "You should be really good because your brother/sister is". The same thing might apply to maths or English, music or anything else.

Write in on the feedback button if you have something to share about being a twin or a triplet and we'll add your comments to this topic.

Dr Kate says

Dr KateBeing a twin can be really interesting to people who are doing research about health and behaviour. It might be possible to tell if some diseases happen more often if you have exactly the same genes.

Some identical twins have reported sensing when their twin has been hurt or feels sad. Some have even talked about feeling the pain for their twin even when they themselves were not hurt or sick. Don't think I'd like that! 

There are a few stories of twins who have been adopted by different families at birth and who have never seen each other until many years later. When they have met they have discovered all sorts of similarities in their lives.

I wonder if I have a brother somewhere?

Some famous twins

Twins, twins, twins
Can drive you nuts
May look the same 
Can't tell who they are!
One likes music, the other sport
People say, "Twins you poor things"
But I don't care I like being a twin


"I have friends who are twins - they look a bit alike but are not exactly the same.'

"My friends are twins. They are a boy and a girl. They do look like each other"           

"When I was back in fourth grade, there were triplets in my class, one girl and two boys. Even though the boys were fraternal I couldn't tell the two boys apart when I was looking at them from the back." (Comment from feedback).

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We've provided this information to help you to understand important things about staying healthy and happy. However, if you feel sick or unhappy, it is important to tell your mum or dad, a teacher or another grown-up.


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