Facts and Mysteries About Identical Twins (2022)

While they may look alike, identical twins are unique individuals with their own personalities and interests.

Identical twins, also known as monozygotic twins, share the same egg at conception and are always either both boys or both girls. Fraternal twins, also known as dizygotic twins, come from two separate eggs fertilized at the same time. They could be the same sex or different.

Factors that increase the chances of having twins include the use of fertility drugs or treatments, a maternal age of over 30 years old, and a family history of twins or multiples. Twins and multiple pregnancy babies are at increased risk of being born prematurely and with low birth weight.

This article will discuss common misconceptions about identical twins. It will also describe their similarities and differences, as well as tips for parenting twins.

Facts and Mysteries About Identical Twins (1)

What You Need to Know About a Twin Pregnancy

Types of Twins

The two types of twins are identical and fraternal. They differ in the way they are conceived and their genetic makeup.

Fraternal vs. Identical

Identical twins share 100% of their genes. They are always born of the same sex. It can be challenging to tell identical twins apart. Whereas fraternal twins often look more like siblings than twins. They share 50% of their genes and could be of the same or different sexes at birth.

Conception

The differences between identical and fraternal twins are due to how they are conceived. When identical twins are conceived, the fertilized egg splits into two, causing two separate embryos to grow. When fraternal twins are conceived, two eggs are fertilized at the same time.

Factors that increase your chances of having twins include:

  • Family history of multiple pregnancies
  • Maternal age of over 30
  • History of past pregnancies
  • Use of reproductive technologies like ovulation-stimulating medicines and in vitro fertilization (IVF)

What Are Conjoined Twins?

Third Twin Theory

There is a theory that there is a third type of twin in between identical and fraternal. Semi-identical twins are a rare type of twins who share 100% of the genes from their mother but only 50% to 75% of the genes from their father. How is this possible? Well, the theory is that when two separate sperm fertilize the same egg and the egg splits into two embryos, you get semi-identical twins.

The Basics of Genes, DNA, and Chromosomes

Role of Twin Genes in Family History

You may have heard that twins run in families. However, experts believe that conceiving twins is affected by genetic and environmental factors. Identical twins make up about 3% to 4% of live births in the United States. The cause of having identical twins is usually unknown.

Fraternal twins, on the other hand, may run in families. Fraternal twins make up about 6% to 8% of live births in the United States. A woman who has a mother or sister who had fraternal twins is twice as likely to have them herself.

(Video) Strange Facts You Never Knew About Twins

Fraternal twins happen when a woman releases multiple eggs (instead of one) during the menstrual cycle, which is known as hyperovulation, and may run in families. Factors that increase your risk of hyperovulation include:

  • Maternal age
  • Race
  • Ethnicity
  • Body composition
  • Number of previous pregnancies
  • Use of reproductive technology

Benefits of Identical Twin Studies

Identical twins are incredibly helpful to researchers when they choose to participate in twin studies. Health researchers often examine the influence of both our genetic makeups and our environments to understand the causes of health conditions. This is often referred to as “nature or nurture.”

Because identical twins share 100% of their genes, we can assume that any differences between the two of them are related to environmental factors. Twin studies in the past have examined up to 18,000 human traits such as height, weight, and chronic diseases to determine how influenced they are by our genes or our environment.

Identical Twin Statistics

The identical twin birth rate in the United States is 32.1 per 1,000 live births. In 2019, about 120,291 sets of twins were born.

Testing, Growth, and Birth

A twin pregnancy is typically more complicated than a singleton pregnancy (with one baby). Twin pregnancies require more frequent prenatal health visits and tests.

The first prenatal test to consider is diagnosing a twin pregnancy. Research suggests that up to 40% of twin pregnancies are not diagnosed until the 13th week of pregnancy. An ultrasound can determine if twin babies are identical or fraternal.

Twin pregnancies are also more likely to end in preterm delivery. Preterm delivery occurs before 37 weeks gestation. Full gestation is 40 weeks. One of the reasons why twins are more likely to be born early is because the usual medical interventions that prevent preterm labor in singleton pregnancies are not effective for twin pregnancies. Because twins are more likely to be born early, they are also more likely to be considered low-birth-weight.

Labor and delivery are different and more complicated for twin pregnancies as well. For a twin pregnancy, the mother is usually taken to the operating room instead of a standard delivery room. This is because twin pregnancies are more likely to require cesarean section (C-section) surgery. However, it is possible for mothers of twins to deliver vaginally. Talk with your healthcare provider about how to prepare.

What Happens Each Week During Pregnancy?

Parenting Identical Twins

Parenting identical twins comes with its own special challenges and rewards. It is helpful to prepare for twins’ unique parenting needs before they arrive and as they grow.

Special considerations when raising twins:

  • Feeding challenges: Because twins are more likely to be born prematurely, they have serious nutritional needs as newborns, and it can be challenging to keep up with feeding both babies.
  • Financial pressures: Parents of twins often need to buy double the diapers, clothing, formula, baby food, and equipment as parents of single babies.
  • Social needs: While twins may look alike, they are different people with unique personalities. Twins are often grouped together but benefit when adults treat them as individuals and encourage them to pursue their interests separately.
  • Sibling jealousy: Twins can be quite time-consuming, and older siblings may feel left out. Try to include your other children in the care of the twins and make some special time for them.

How parents and caregivers can support their twins:

  • Plan alone time: Parenting twins is demanding, and it can be difficult to spend alone time with each child. As often as you are able, spend time with one twin at a time to give them the attention they crave.
  • Encourage individualism: Give your twins a chance to develop their own personalities outside of one another by encouraging them to pursue their own interests and play with their own friends. This may also help to reduce the chance that your twins become overly competitive with or interdependent on each other.
  • Make a school plan: Once your twins are old enough for school, work with their teachers to determine if they should be in the same class or separate classes.

Parenting twins can be both incredibly rewarding and exhausting. It is important to keep your own needs in mind, such as:

  • Socialization: It is often more difficult for twin parents to get out of the house and see their friends. Seek support where you can.
  • Mental health support: Postpartum depression (PPD) is more common in women who have had twins. Know the signs of PPD and talk with your healthcare provider if you are concerned.
  • Financial resources: It’s estimated that the healthcare delivery cost for a twin birth is four times higher than for singleton births. Check with your insurance company and hospital billing department to understand your out-of-pocket costs.
  • Rest: Caring for twins is physically demanding and emotionally stressful. As often as you can, take time to rest and catch up on sleep.

How to Tell Your Twins Apart

Even parents can have a difficult time telling their identical twins apart. To tell newborn twins apart, try color-coding their clothing or using name bracelets. As they age, their unique personalities will tell them apart.

Summary

Identical twins have fascinated researchers and parents for decades. When they are conceived, a single fertilized egg splits into two embryos. While identical twins look alike, their personalities, interests, and needs can be very different.

A Word From Verywell

If you are a parent to twins, you know how much joy they can bring to your life. It’s also helpful to name the unique challenges so that you can seek out the support you need. When your twins are babies, ask for help with childcare, cooking meals, house cleaning, and other tasks.

(Video) 10 Things You Didn't Know About Identical Twins (by identical twins)

Frequently Asked Questions

  • Do identical twins read each other’s minds?

    Identical twins have unique ways of communicating with one another. While they cannot actually read each other’s minds, they learn each other’s facial expressions and gestures because they spend so much time together. This gives them unique insight into each other.

  • Are identical twins rare?

    Identical twins make up about 3% of live births in the United States.

  • Which parent passes on the twin gene?

    Fraternal twins tend to run in families. This may be due to hyperovulation, releasing more than one egg during the menstrual cycle, which is genetic. Because the mother is the one who ovulates, she is the one who is responsible for the increased chance of twins.

  • What are other ways to tell identical twins apart?

    Identical twins can be especially difficult to tell apart as newborns, even for their parents. If you are concerned about telling your babies apart, consider color-coding their clothing or having them wear bracelets with their names on them. As they age, their unique personalities will help to distinguish them from one another.

13 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. MedlinePlus. Twins, triplets, multiple births.

  2. National Human Genome Research Institute. Identical twins.

  3. National Human Genome Research Institute. Fraternal twins.

  4. University of Rochester Medical Center. Overview of multiple pregnancy.

  5. Gabbett MT, Laporte J, Sekar R, et al. Molecular support for heterogonesis resulting in sesquizygotic twinning. N Engl J Med. 2019;380(9):842-849. doi:10.1056/NEJMoa1701313.

  6. Centers for Disease Control and Prevention. FastStats - multiple births.

  7. MedlinePlus. Is the probability of having twins determined by genetics?

  8. Sahu M, Prasuna JG. Twin studies: a unique epidemiological tool. Indian J Community Med. 2016;41(3):177-182. doi:10.4103/0970-0218.183593

  9. Polderman TJ, Benyamin B, de Leeuw CA, et al. Meta-analysis of the heritability of human traits based on fifty years of twin studies. Nat Genet. 2015;47(7):702-709. doi:10.1038/ng.3285

  10. Monni G, Iuculano A, Zoppi MA. Screening and invasive testing in twins. J Clin Med. 2014;29;3(3):865-882. doi:10.3390/jcm3030865

  11. Johns Hopkins Medicine. Twin pregnancy: answers from an expert.

  12. American Academy of Pediatrics. Preparing for twins.

    (Video) 25 STRANGE Facts About Twins You Might Not Know

  13. American Society for Reproductive Medicine. Challenges of parenting multiples.

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Facts and Mysteries About Identical Twins (2)

By Carrie Madormo, RN, MPH
Carrie Madormo, RN, MPH, is a health writer with over a decade of experience working as a registered nurse. She has practicedin a variety of settings including pediatrics, oncology, chronic pain, and public health.

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FAQs

What is special about identical twins? ›

While they may look alike, identical twins are unique individuals with their own personalities and interests. Identical twins, also known as monozygotic twins, share the same egg at conception and are always either both boys or both girls.

Are identical twins 100% genetically the same? ›

The study of 381 pairs of identical twins and two sets of identical triplets found that only 38 were genetically identical, Tina Hesman Saey reports for Science News. Most had just a few points of genetic mismatch, but 39 had more than 100 differences in their DNA.

What is the most common gender in identical twins? ›

Identical (monozygotic) twins happen when a single egg (zygote) is fertilised. The egg then divides in 2, creating identical twins who share the same genes. Identical twins are always the same sex, so if your twins are identical, you'll have 2 girls or 2 boys.

How rare is it to be an identical twin? ›

The chances of having identical twins is relatively rare — around 3 or 4 in every 1,000 births. And while it may be obvious, identical twins are always the same sex, either both boys or both girls, at birth. Why?

What are identical twins called? ›

Identical or 'monozygotic' twins

Twins conceived from one egg and one sperm are called identical or 'monozygotic' (one-cell) twins. The biological mechanisms that prompt the single fertilised egg to split in two remain a mystery.

What Do identical twins have in common? ›

Identical twins (also called monozygotic twins) result from the fertilization of a single egg by a single sperm, with the fertilized egg then splitting into two. Identical twins share the same genomes and are always of the same sex.

Who is bigger in twins? ›

As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood.

Who carries twin gene? ›

However, for a given pregnancy, only the mother's genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father's genes can't make a woman release two eggs. It sounds like fraternal twins do indeed run in your family!

Do identical twins have the same fingerprints? ›

But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints. Like physical appearance and personality, fingerprints are largely shaped by a persons DNA and by a variety of environmental forces.

What are the rarest type of twins? ›

Monoamniotic-monochorionic Twins

This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.

What celebrity has an identical twin? ›

Bohemian Rhapsody star Rami Malek has an identical twin brother, Sami Malek. Rami brought Sami to the Golden Globes in 2019, shocking fans who were surprised to learn the actor has a twin. Despite his appearance at the awards show, Sami isn't in the entertainment industry, and instead works as a teacher.

Can a boy and a girl be identical twins? ›

In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.

Do twins have the same blood type? ›

Monozygotic (identical) twins will have the same blood type, with a few very rare exceptions. Dizygotic (fraternal) twins may have the same blood type, or they may have different types. Therefore, it may be concluded that twins with differing blood types are dizygotic, or fraternal.

Can a twin have twins? ›

According to The American Society for Reproductive Medicine, women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins. It was previously believed that identical (monozygotic) twins were random — not genetic.

Do twins have exact DNA? ›

In effect, though identical twins don't have identical DNA, they are genetically similar.

Who were the first identical twins? ›

The sisters were born on Nov. 5, 1913. Two sisters in Japan have been declared the world's oldest identical twins, at age 107, according to news reports.

Do twins have the same intelligence? ›

Can we conclude that intelligence isn't inherited? The answer to this question is "no." The reason for this is that variation in intelligence may be grounded in genetic material that identical twins do not share. So the environment could affect intelligence a lot less than we once thought.

Where Do identical twins come from? ›

Monozygotic (MZ) twins, also called identical twins, occur when a single egg cell is fertilized by a single sperm cell. The resulting zygote splits into two very early in development, leading to the formation of two separate embryos.

Why do mothers of twins live longer? ›

"Shorter birth interval is an indication of the physical health of the mother," Smith said. The reproductive span -- age at last birth minus age at first birth -- was longer for mothers of twins, even when controlling for age of marriage.

Do twins communicate in the womb? ›

The results suggest that twin fetuses are aware of their counterparts in the womb, that they prefer to interact with them, and that they respond to them in special ways. Contact between them appeared to be planned—not an accidental outcome of spatial proximity, says study co-author Cristina Becchio of Turin.

Do identical twins have the same personality? ›

Thus identical twins, though they start with the same genes, likely develop different personalities in the same environment partially based on how they interact with their environment.

Can twins have different fathers? ›

But you may be left wondering: Can twins have different fathers? The answer is yes, but only in cases in which they're fraternal, as identical twins form from a single egg/sperm combination and thus cannot have different fathers.

Is the first born twin stronger? ›

Abstract. Despite the clinical impression that firstborn twins do better than second-born twins, recent reports have shown no difference in perinatal mortality between them.

What happens if twins have a baby? ›

"Twins married to twins who both have babies at the same time." Since identical twins share the same DNA, the children of two pairs of identical twins are legally cousins, but genetically more similar to siblings.

Can twins have different mothers? ›

It sounds impossible. But thanks to the reproductive advancements of surrogacy and in vitro fertilization, twins Connor and Cameron Payne were born to different mothers 16 days apart in different hospitals. Kathy and Ray Payne wanted children and had tried for eight years to make it happen.

Can identical twins look different? ›

Yes! Identical twins came from the same sperm and egg, so they have the same chromosomes and genes. But there are environmental differences that can affect the way they look and behave.

Can identical twins read others minds? ›

There is no evidence of twin telepathy.

One of the more frequent mythconceptions is whether twins can read each other's minds.

Can an identical twin be taller? ›

Identical twins can help answer this type of question. For example, we know that identical twins can be different heights. This means height can't be controlled by your genes alone, because identical twins have the same genes. So height must be part nature and part nurture.

Do twins skip a generation? ›

It's a common misconception that twins skip a generation in families. There is absolutely no evidence, other than circumstantial, that twins are more likely to occur every other generation.

Are twins attracted to each other? ›

Relatives who meet when they're adults aren't equipped with blockades. Research done on twins have found instances of fraternal twins, who were separated at birth, but met each other much later. According to researchers, more than anything, they are likely attracted to each other's similarities.

What percentage of identical twins are girls? ›

Also, it does not distinguish between multiples conceived spontaneously or with fertility assistance, which could affect the pregnancy outcome. More than two-thirds of the twin sets in the study were male-female pairs, with about 15% being same-sex twin sets.

What are a boy and girl twins called? ›

If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA. A boy has XY chromosomes and a girl has XX chromosomes.

How old are the beautiful twins now? ›

Profile summary
Full namesLeah Rose and Ava Marie Clements
Age12 years old (as of 2022)
Zodiac signCancer
Place of birthOrange County, California, USA
Current residenceUnited States of America
14 more rows
13 Aug 2022

What did the famous twins do? ›

Signed-in readers now can bookmark stories to read later. NEW! A pair of Mobile twins who are TikTok famous were arrested Thursday after they allegedly fired guns in a local park, wounding two people, including a teenage girl, police said.

Can twins have different birthdays? ›

For the most part, twins and multiples share the same birthday. However, depending on the time of day the babies are born and how long the timespan is between each baby's birth, twins can be born on different days.

Can identical twins be handed? ›

In about 21% of identical (monozygotic or MZ) twin pairs, one twin is right-handed and the other is either left-handed or ambidextrous. Since identical twins share identical genes, this is evidence that handedness is not a totally genetic trait.

Can identical twins have different eye colors? ›

The possibility of identical twins having different eye colors is extremely rare. Fraternal twins (developing from 2 separate sets of egg and sperm) however can most definitely have different eye colors as they only share about 50% of their DNA with their twin, just like any other siblings do.

How are identical twins different from each other? ›

That's because so-called identical twins pick up genetic mutations in the womb, as their cells weave new strands of DNA and then split into more and more cells. On average, pairs of twins have genomes that differ by an average of 5.2 mutations that occur early in development, according to a new study.

Can identical twins read others minds? ›

There is no evidence of twin telepathy.

One of the more frequent mythconceptions is whether twins can read each other's minds.

What are the benefits of having twins? ›

What are the benefits of having twins?
  • One pregnancy.
  • One delivery.
  • Double love.
  • Built in teammate.
  • Same sex twins can share clothes.
  • Sharing.
  • People tend to be nicer.
  • More gifts.
5 Apr 2021

Do twins bring good luck? ›

TAIWO and KEHINDE

““We believe 'Ibeji' (twins) bring good luck. They represent fertility and bring love, they are a blessing to the family. Once you have twins, people believe that more and more of everything will come to you. Twins are also related to the monkey spirit and more specifically to the Edun monkey.

Do identical twins have the same personality? ›

Thus identical twins, though they start with the same genes, likely develop different personalities in the same environment partially based on how they interact with their environment.

Can identical twins be male and female? ›

In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.

Do identical twins have the same health problems? ›

Not necessarily. Identical twins may differ on a host of diseases and conditions. According to Haseley, “If a genetic change occurs in a gene that affects its function, health concerns may arise.” Twins may differ in their risk of cancer, rheumatoid arthritis or other diseases.

What powers do twins have? ›

Wonder Twins
SpeciesExxorian
Place of originExxor
Team affiliationsSuper Friends Justice League Ten Elements of the Universe Extreme Justice
AbilitiesZan can transform into any form of water Jayna can transform into any animal.
7 more rows

Do twins have spiritual powers? ›

In parts of West Africa, twins are believed to hold spiritual powers. “Many people will seek blessing from them,” Babajanyan said. “So, their mothers, often from poor [households] bring them out, usually around mosques, for alms and donations.

Can twins feel when the other dies? ›

Twins literally do not know how to exist as one. When a twin dies, the twinless twin longs to reconnect. The twinless twin may have phantom pain or feel half dead. He or she may feel a need to represent both him or herself and the deceased twin or may even take on behaviors of the deceased twin.

Does the Bible say anything about twins? ›

"And when her (Rebekah) days to be delivered were fulfilled, behold, there were twins in her womb. And the first came out red, all over like a hairy garment; and they called his name Esau. And after that came his brother out, his hand holding on to Esau's heel – " (Gen 25:24-26).

Do mothers of twins live longer? ›

For women born 1870-1899, moms of twins averaged reproductive spans of 14 years 11 months versus 14 years for singleton moms. Both results were statistically significant. Moms of twins also were older at the time of their last birth.

What does a twin symbolize? ›

Twins symbolize the first and last relationship: life and death.

Which month are twins born? ›

Twins are more likely to be born early, often before 38 weeks, so it's important to understand your birth options. Less than half of all twin pregnancies last beyond 37 weeks.

Do twins bond in the womb? ›

Getting twins to bond isn't always easy, even though their bond potentially started in the womb. Parents often struggle to get their two babies to get along because both babies need individual attention that may be required at different times, according to Everyday Family, a parenting advice website.

Do twins live to be the same age? ›

Even twins, identical twins, die at different times.” On average, he said, more than 10 years apart.

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