Do twins run in families?

Along with the surprise and excitement of having twins comes the inevitable question from friends and strangers: do twins run in your family?

The idea that twins run in families is a widely accepted notion – but is it fact or fiction?

Here, we discuss whether twins run in families, and the factors that can increase your chances of conceiving twins.  

Do twins run in families? Are twins hereditary?

Whether or not you can say twins run in your family depends largely on the type of twins you have in your family.

There are two main types of twins: monozygotic (identical twins) and dizygotic (non-identical or fraternal twins).

Monozygotic (identical) twins occur when a single fertilised egg splits into two, resulting in two separate embryos. Identical twins share near-identical DNA profiles, with very minor variations that are extremely difficult to detect.

Identical twins do not run in families. This means that if you are trying to conceive, you have a 1 in 250 chance of conceiving identical twins, with the odds being the same for everyone.

Dizygotic (fraternal or non-identical) twins occur when two eggs are released during ovulation, and both eggs are fertilised, developing as separate embryos.

Non-identical twins share approximately the same amount of DNA as siblings from different births.

However, non-identical twins can run in families and, if you are a woman trying to conceive, your likelihood of conceiving non-identical twins is increased if you have a history of these types of twins in your family.

This is because some women are born with a genetic predisposition towards hyperovulation: where more than one egg is released during each menstrual cycle.

If a man inherits the hyperovulation gene from his mother, this does not increase his chances of conceiving non-identical twins. However, he may pass this gene onto his daughter. She in turn is more likely to release more than one egg when she ovulates and could therefore conceive non-identical/fraternal twins.

Do twins skip a generation?

Twins can skip a generation. This is due to something called hyperovulation: an inherited trait that can predispose some women to release more than one egg during each menstrual cycle.

Dizygotic (fraternal or non-identical) twins occur when two eggs are released during ovulation, and both eggs are fertilised, developing as separate embryos.

This means that a woman who is predisposed to hyperovulation has an increased chance of conceiving non-identical twins.

If a woman with hyperovulation has a male child, he may still inherit the gene for hyperovulation. However, as he cannot ovulate, this means he is no more likely to conceive twins than the general population.

If the man has daughters however, he may pass the genetic predisposition to hyperovulation onto them. This means that there is an increased likelihood of them conceiving non-identical (fraternal) twins.

Below is an example of how non-identical twins can skip a generation:

• Generation 1: has twins.

  A woman with hyperovulation gives birth to non-identical (dizygotic/fraternal) twin boys. Each boy inherits the hyperovulation trait

• Generation 2: does not have twins.

  The boys grow up to have children with women who do not have hyperovulation gene. This means they are no more likely than the rest of the population to have a pregnancy with multiple births. However, each of the boys has a daughter to whom they pass on their mother’s hyperovulation gene

• Generation 3: has twins.

  The girls with the hyperovulation gene inherited from their father/grandmother may go on to have non-identical (dizygotic/fraternal) twins themselves – meaning the twins have skipped a generation

Which side of the family can influence your chances of having twins?

If you are a woman with a history of non-identical twins on either side of your family (mother’s or father’s), there is an increased chance of you conceiving non-identical twins.

This is because the gene for hyperovulation – where more than one egg is released during each menstrual cycle – can be inherited from your mother or your father.

Dizygotic (fraternal or non-identical) twins occur when two eggs are released during ovulation and are both fertilised, developing as separate embryos.

If you are a man with non-identical twins on your mother’s side, this does not increase your chances of conceiving twins. However, you can still pass the hyperovulation gene onto any female children you might have, meaning their chance of having non-identical twins will be increased.

What type of twins runs in families?

Dizygotic (fraternal or non-identical) twins occur when two eggs are released during ovulation, and both eggs are fertilised, developing as separate embryos.

These are the types of twins that can run in families. For women, your likelihood of conceiving non-identical twins is increased if you have a history of these types of twins in your family.

How common is it to have twins?

According to the Health Service Executive (HSE), around 2 per cent of births in Ireland are twins.

Globally, twinning rates have increased from 9 to 12 per 1,000 births since the 1980s, with the greatest rises seen in North America, Europe and Asia.

Fraternal twins are more common: with two-thirds of all twins being fraternal/non-identical/dizygotic, and one-third being identical/monozygotic.

What other factors contribute to having twins?

As well as hyperovulation, there are other factors that can increase your chances of conceiving non-identical twins, including:

• The mother’s age: women over the age of 35 are more likely to release multiple eggs during the one menstrual cycle, which increases the chances of conceiving non-identical twins
• Ethnicity: non-identical twins are more common among certain ethnic groups, with Africa having the highest rate of twin births
• Fertility treatments: fertility treatments such as IVF can increase your chances of conceiving twins, as more than one embryo is sometimes transferred during the procedure. There’s also the chance of a single embryo splitting, leading to identical twins

How can I get a DNA test for twins?

It’s easy to order an AlphaBiolabs Twin DNA Test online now, for just €139.

Your test kit will contain everything you need to collect the DNA samples at home and return them to our laboratory.

Your secure, password-protected results will be emailed to you in 2-3 working days.

It’s important to remember that consent is needed from or on behalf of anyone submitting their DNA samples for testing.

Anyone aged 16 or over may provide their own consent for the test to take place. When testing children under 16 years of age, consent must be provided by a parent or guardian with guardianship for the child(ren).

Need more information on our Twin DNA Test? Call our Customer Services team on 01 402 9466 or email info@alphabiolabs.ie.