How Rare are Twin Babies Exactly

There are 360,000 newborns that are born every day according to the United Nations. As a twin parent, we never went in expecting to have twins so were pleasantly surprised when we found out the good and slightly scary news – we were having twins!

But how rare is having twins exactly? Good question. This article looks to explore this question in great detail. We’ll look into the increasing number of people turning to fertility treatments and how this can increase twin numbers while also looking at how rare having twins naturally can be.

Are Twin Babies Rare?  

Short answer – Yes! But becoming less so.

Over the last 25 years, we’ve seen a rise in the number of twins being born which we can attribute to a variety of reasons. In fact, the chances of having twin babies have increased to 32.6 per 1,000 births.  

Why are we seeing the number of twins being born increasing?  In some cases we are seeing a gradual change in how people are having babies where they are now trying later in life or using fertility treatments whilst we are also learning more about the contributing factors that cause people to have twins. Some of these reasons that increase your chances of having twins include:

  • Women who wait to have kids after 35 years old are most likely to have twins
  • Rise of fertility treatment increases your chance of having twins
  • We know now that race (particularly African) have greater chances of having twins
  • Greater understanding of family history to know when twins run in the family
  • Being overweight can also contribute to having twins

But what about the different types of twins you can have? There are two types of twins you can have which includes the more associated type of twins – identical or otherwise known as monozygotic and fraternal twins otherwise known as dizygotic twins. We know that fraternal rates occur in about 70% of twin births whilst identical twins make up the remaining 30% of twin births.

Fraternal Twins (Dizygotic)

If a woman is pregnant with twins, it is more common for them to give birth to fraternal twins. Fraternal twins are no different from having siblings that are born years apart. You can have two girls, two boys, or a boy and a girl. They will generally share looks similar to how a siblings would share looks without being identical.

Fraternal twins occur when two eggs are fertilized separately by two sperm cells. They don’t share the same DNA, which makes them similar to siblings that are not born together. 

How Common is it to Have Fraternal Twins?

Fraternal twins are more likely to occur due to genetics (e.g. running in your family where your mother was a twin) and also due to environmental factors.  We know that fraternal twins are twice as common as identical twins and women who have a mother or sister that are twins are more than twice as likely to have twins themselves.

Identical Twins (Monozygotic)

Having identical twins is rare with the rate estimated to be about 1 in 250 pregnancies in Australia being identical twins. Unlike fraternal twins, identical twins are always the same sex, either two boys or two girls. There are three different types of identical twins that occur during pregnancy:

  1. Dichorionic diamniotic (DCDA) – The twins have their own placenta, inner membrane and outer membrane.
  2. Monochorioinic diamniotic (MCDA) – The twins share the same placenta and chorion but will have their own amnion.
  3. Monochorionic monoamniotic (MCMA) – The twins share everything.

For the purpose of this article, we aren’t going to go into great detail about each of the above and what this means for your pregnancy. We’d recommend Twins Australia as a great guide that explores this topic in great detail.

How Common is it to Have Identical Twins?

Identical twins or monozygotic twins are different to fraternal twins which commonly run in the family (genetics) and also caused by environmental factors.  Instead it is thought that genetics play less of a role in the birth of identical twins and the cause is more linked to environmental factors.

Risks Associated with Having Twins

Having twins comes with an increased level of risks vs. someone having a singleton pregnancy. Some of the risks we continue to see in twin pregnancies include:

  • Increased risk of getting gestational diabetes
  • Twice as common to develop anemia vs a singleton pregnancy
  • Twice the risk of your twins developing birth defects such as spina bifida and other neural tube defects
  • Increased risk of having a miscarriage which is sometimes also referred to the vanishing twin syndrome that occurs during the first trimester.
  • Increased risk of twin to twin transfusion syndrome when twins share the same placenta. This results in one twin receiving more blood and nutrients than the other twin which can result in your twins needing to be delivered early.
  • Increased risk of cord entanglement of one of your twins
  • Greater risk of postpartum hemorrhage for the mother after giving birth.

If you’re reading the above and slightly freaking out, you’ll be pleased to know that with the increased number of twins being born, this helps us better understand how we can identify some of these risks early so they can be properly tracked and managed throughout the pregnancy. If your scans detect any of the above, it’s likely your doctor will recommend you have more scans so these risks can be carefully monitored throughout the pregnancy.

Conclusion

With the rate of twins being 1 in every 250 pregnancies we can confirm that having twins is rare. Depending on what type of twins you are having (dizygotic vs monozygotic) you may find your twins are even more rarer.

As a twin parent I can safely say that having twins is one of those most amazing things you’ll experience. Sure, it can be super tough having two babies when most of your friends only have one and can’t really relate to what it must be like having two babies at the same time.

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