Types of twins and your chances of having multiples

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 (main) types of twins – fraternal and identical.

Types of Twins: 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.

Please note: DCDA twins can still be identical, the fertilised egg splits really early (1-3 days).

Types of Twins: Identical twins

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.

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.

The Science Behind Identical Twins?

Identical twins are one of nature’s most fascinating little miracles. But how exactly do they form? And why is it so hard to tell if twins are identical or not during pregnancy?

Let’s break it down in a way that makes sense (and skip the heavy science jargon wherever we can!).

One Egg, One Sperm… Then a Twist

All pregnancies begin the same way. One egg, fertilised by one sperm. This fertilised egg is called a zygote.

In some rare cases, that single zygote splits. When it does, it can create identical twins or identical triplets. This is known as monozygotic twinning (“mono” meaning one, and “zygotic” referring to the single fertilised egg).

Timing is Everything

The way the egg splits plays a huge role in how the pregnancy develops. It actually affects how many placentas and amniotic sacs the babies will have. This can impact the risks, monitoring, and even delivery plans.

Here’s how the timing works:

• Split within the first 3 days:
  ➤ Each twin develops its own placenta and amniotic sac
  ➤ Called DCDA twins (Dichorionic, Diamniotic)
• Split between days 4 to 8:
  ➤ Twins share a placenta, but each has a separate amniotic sac
  ➤ Known as MCDA twins (Monochorionic, Diamniotic)
• Split between days 9 to 13:
  ➤ Twins share both the placenta and amniotic sac
  ➤ Termed MoMo twins (Monochorionic, Monoamniotic)
• Split after day 13:
  ➤ The separation is incomplete, resulting in conjoined twins

So… Can You Tell if Twins Are Identical Before Birth?

Short answer? Not always.

Even with today’s advanced ultrasounds, the placenta and sacs don’t always reveal the whole picture. Health professionals can (and do!) occasionally misclassify twins as fraternal (non-identical), especially early on.

That’s why many parents of “lookalike” twins end up confused when strangers constantly ask, “Are you sure they’re not identical?”

The Only Way to Know for Sure

If you’re eager to find out whether your twins are identical or fraternal, a DNA test is the most accurate option. It’s painless, non-invasive, and gives you a clear answer — no more guessing or second-guessing every time someone comments on how alike they look!

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.

Cord Blood Banking for Twins

One question that gets asked a lot is about cord blood baking for twins.

Your twins umbilical cord blood and tissue contains powerful stem cells that can be used for medical treatments. Cord blood is currently being used in place of bone marrow transplants for many life-threatening conditions such as blood cancers, leukaemia’s, immune system and metabolic disorders.

Request your free information pack HERE.

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