Types of twins and your chances of having multiples

kinds of twins

Finding out you are expecting twins can be a bit of a shock to the system. You go into the appointment hoping to hear a heartbeat and you come out hearing two! One of your first questions may be about the different types of twins.

After you get over the initial shock, you might find that having twins has a lot of upsides. If you were hoping for a family consisting of two children, then you will only have to go through the birthing process once. The other upside is your children will always a have friend and companion to play with and share their life with. Someone who gets them and will always be at the same life stage.

There are two types of twins – fraternal and identical.

Fraternal twins

Fraternal twins are formed from the fertilization of two eggs and grow in separate placentas and have separate inner and outer membranes. They are also known as ‘dichorionic diamniotic’ (DCDA) twins or ‘dizygotic twins. Fraternal twins are not identical and can be the same or different sex. For example, a boy and a girl twin are fraternal twins.

Types of twins

Identical twins

Identical twins are formed from the same egg which splits after conception and are also known as ‘monozygotic twins’. These type of twins share the same placenta and the same outer membrane. Monochorionic monoamniotic (MCMA) twins also share the same inner membranes, while monochorionic diamniotic (MCDA) twins have different inner membranes. Identical twins share the same genetic makeup and DNA hence they look the same. Identical twins however, can develop different personalities and act unique to each other.

main types of twins

A sub-set of twins to identical twins is mirror twins. Mirror twins are the result of the egg splitting between days 9-12 of conception and each twin will be a mirror of the other. For example, one will be right handed and one will be left handed. In some rare cases, this can also result in one twins organs being mirrored i.e. heart beating on the right side.

To find out more about the different types of twins, please read our blog post on Common Multiple Birth Terms.

What are my chances of having twins?

Twins can run in families and fraternal twins are genetic whereas identical twins are not. The chances of having twins comes from the mother’s side as she is the one who will carry the gene to release more than one egg at ovulation. As identical twins are the result of one egg splitting, they are not considered genetic. If you have a history of twins in your family, then you are every chance to have twins yourself.

Twins are always of interest to people scientists and the general population for their similarities and differences combined.  Having twins is a blessing you will be proud to share.


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