Key things to know about twin pregnancy: the facts and figures

In 2024, there were 8957 sets of twins and 130 sets of triplets born in the UK.

Data sources: Office for National Statistics (England and Wales), National Records of Scotland and Northern Ireland Statistics and Research Agency. A full regional breakdown can be found at the bottom of the page.

These figures highlight why it's so important that families expecting twins, triplets or more receive specialist care and support throughout pregnancy.

Over the past 20 years, the number of multiple births initially increased. This was influenced by a number of factors, including women having children later in life, the increased use of fertility treatment and improvements in neonatal care.

Over the last 10–15 years, however, the rate has levelled off and has more recently declined alongside the overall fall in birth rates. This is largely due to changes in fertility practice, particularly the move towards single embryo transfer during IVF treatment.

With around 653,000 pregnancies in the UK in 2024, around 1 in every 72 pregnancies resulted in twins or triplets.

What are the chances of having twins or triplets?

The likelihood of having twins or triplets depends on several factors, including your age, family history, ethnicity and whether you have fertility treatment.

Most pregnancies result in one baby. Naturally conceived multiple pregnancies occur in around 1–2% of pregnancies, while fertility treatment, including IVF, can increase the chance of a multiple pregnancy. Thanks to changes in fertility practice, however, IVF-related multiple pregnancies are much less common than they were in the past.

How common are identical twins?

Identical (monozygotic) twins happen when a single fertilised egg splits into two embryos. They:

• Occur in around 1 in every 250 pregnancies (around 0.4%)
• Do not run in families
• Share almost identical genetic material
• May share one placenta or have separate placentas, depending on when the embryo splits
• Can differ in size, personality and temperament because of environmental influences and individual development

Identical twinning happens randomly and is not thought to be inherited.

What Are Mirror Twins and How Are They Different from Identical or Fraternal Twins?

Mirror twins are a rare type of identical (monozygotic) twins whose physical traits appear as mirror images of one another. For example, they may have birthmarks on opposite sides of their bodies, opposite dominant hands, or other features that are reversed from one twin to the other.

Like all identical twins, mirror twins develop from a single fertilised egg and therefore share the same genetic makeup. However, scientists do not fully understand why some identical twins exhibit these mirrored characteristics. One theory suggests that mirror twinning occurs when the fertilised egg splits later than usual during early development.

Typically, an egg divides within the first week after conception. In some cases, however, the split may occur between seven and ten days after fertilisation, which could contribute to the development of mirrored features. Despite this theory, researchers have not yet determined the exact cause of mirror-image twinning.

Can you have twins more than once?

Whether you're likely to have twins again depends on whether your first twins were identical or non-identical.

If you've had identical twins

If your twins were identical, your chance of having another identical twin pregnancy is similar to anyone else's—around 1 in 250 pregnancies.

If you've had non-identical twins

If your twins were non-identical (dizygotic), your chance of having twins again is higher, particularly if there is a family history of non-identical twins.

This is because non-identical twinning is linked to hyperovulation—a tendency to release more than one egg during ovulation—which can run in families.

What's the difference between identical and non-identical twins?

Identical (monozygotic) twins

• Develop from one fertilised egg that splits into two
• Are always the same sex
• Share almost identical genetic material
• Make up around one-third of twin pregnancies
• May share a placenta or each have their own
• Identical triplets and higher-order multiples can also occur, although this is very rare

Non-identical (dizygotic) twins

• Develop when two separate eggs are fertilised by two separate sperm
• Are genetically no more alike than any other brothers and sisters
• Can be two girls, two boys or one of each
• Make up around two-thirds of twin pregnancies

Fertility treatment and multiple pregnancies

In the past, IVF was much more likely to result in a multiple pregnancy because two or more embryos were often transferred to improve the chances of success.

Today, this is much less common. Changes in fertility practice, including the wider use of single embryo transfer, have significantly reduced the number of IVF-related twin and triplet pregnancies.

Current NICE guidance recommends single embryo transfer in many cases, particularly for younger women with a good chance of success. In some circumstances, women aged 40–42 may be offered the transfer of two embryos following discussion with their fertility specialist.

Although uncommon, an embryo transferred during IVF can still split naturally, resulting in identical twins.

Reducing the number of multiple pregnancies following fertility treatment has improved outcomes for both mothers and babies, while helping more families experience safer pregnancies.

Multiple birth statistics by region in 2024