Mirror Identical Twins: What Are They & Their Charactertics

Mirror Twins – Causes & Characteristics

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Dr. Rima Sonpal (Gynecologist/Obstetrician)
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Nowadays, giving birth to twins is fairly common. When you are expecting twins, many parents hope to have a boy and a girl. But, do you know that you can give birth to mirror twins as well? For those wondering what mirror twins are, this article is a must-read.

You must be aware of fraternal twins and identical twins. Fraternal twins are formed when 2 eggs released at the same time are fertilised by two different sperms simultaneously, resulting in 2 genetically different children. Identical twins (monozygotic twins) are formed when one fertilised egg splits into two and develops into 2 babies with the exact same genetic information. Identical twins look very much alike and have the same genetic material.

Mirror Twins or mirror image twins are a type of identical twins. Their features appear on opposite sides, like a mirror image. For example, one mirror twin may have a mole on her left cheek, and the other twin will have the same mole on her right cheek.

What Are Mirror Twins?

Mirror twins or mirror identical twins are twins whose features appear asymmetrically or on the opposite sides. Identical twins have the same sex and share the same blood type. Mirror twins have identical but asymmetric physical features. For example, one twin could be left-handed, and the other could be right-handed. In extreme cases, mirror twins may have mirrored internal organs, where the placement of internal organs may be reversed in one of the twins.

How Common Are Mirror Twins?

Mirror twins, also known as mirror-image twins or mirror-image identical twins, occur in a small percentage of identical twin pregnancies. The exact prevalence is not well-established, but it is estimated that mirror twins make up about 1-2% of all identical twin births. These twins result from a late split of the fertilized egg, leading to asymmetrical features that appear as mirror images of each other.

Are Mirror Twins Always Identical?

Yes, mirror twins are always identical. They are a subtype of identical (monozygotic) twins and result from a late split of the fertilized egg. As a result, mirror twins share virtually identical genetic material and are of the same sex.

Causes of Mirror Twinning

Mirror image twinning occurs because of the late splitting of the fertilised egg. For regular identical twins, the egg splits into two between 2 and 8 days of conception. In the case of mirror twins, the egg splits into 2 much later, between 9 and 12 days of conception. This causes the twins to mirror each other.

Is There Any Test to Detect a Mirror Pair?

While identical twins can be detected with a DNA test as they share the same genetic material, it is not possible to determine if they are mirror twins by genetic testing. An examination of the physical characteristics has to be done to find out if the identical twins are actually mirror twins.

Mirror Twins

Characteristics of Mirror Image Twins

Mirror image twins may have several characteristics that are reversed. Some of these are:

  • Birthmarks and moles – They may appear asymmetrically in mirror twins. For example, one twin will have a birthmark or mole on the right side of the cheek, and the other will have the same mole on the left cheek. One may have a birthmark on the right leg, while the other will have the exact same birthmark on the left leg.
  • Freckles and dimples – These are also asymmetrical in mirror twins. For example, if one has a dimple on the left side of the chin, the other will have the dimple on the right side of the chin. The pattern of freckles can also be asymmetric in mirror twins.
  • Hand orientation – Hand orientation is usually asymmetric in mirror twins. For example, if one twin is right-handed, the other is usually left-handed.
  • Hair whorls – Mirror twins may have hair whorls in opposite directions. If one twin has hair that swirl clockwise, the other may have hair that swirl counterclockwise.
  • Eye shape and eyebrow shape – Eye shape and eyebrow shape can also be reversed in mirror image twins. For example, if the right eye is slightly smaller in one twin, the left eye of the other twin will be small.
  • Ear shape – Ear shape can also be asymmetric in mirror twins. The ridges and bumps of the outer ear are unique to every individual. This can be reversed in mirror twins.
  • Nostril shape – The shape of the nostrils may also be asymmetric in mirror twins.
  • Organs – In extreme cases, which is rare, the positioning of the internal organs may be opposite in mirror twins. This is called ‘situs inversus’, where internal organs like the heart, stomach or liver are found on the opposite side of their usual anatomical position.
  • Mirror Twins’ Personality – Mirror-image twins may also have opposite personalities. For example, one may be highly introverted, while the other may be an extrovert. One may prefer sleeping on the right side, while the other may prefer sleeping on the left side.
  • Tooth eruption pattern – The order and timing of tooth eruption can be reversed in mirror twins. If one twin’s first tooth emerges on the upper right, the other twin’s first tooth may emerge on the upper left.

Complications With Mirror Twins

Mirror twins, while fascinating in their symmetrical and reversed traits, may be associated with certain complications. These complications can arise due to the unique aspects of their development. Here are some potential complications:

  • Mirror Syndrome: In some cases, complications in one twin can lead to issues in the other, a phenomenon known as mirror syndrome. For example, if one twin develops a health problem, the other may show similar symptoms or be affected in some way.
  • Inversion of Organs (Situs Inversus): Although rare, mirror twins may experience an inversion of internal organs, a condition called situs inversus. This reversal in the positioning of organs could potentially lead to medical challenges.
  • Developmental Delays: Mirror twins might face developmental delays or challenges, possibly due to the unique circumstances of their shared prenatal environment. Monitoring developmental milestones is crucial for timely intervention if needed.
  • Complications During Birth: The reversed and mirrored positioning of features can sometimes lead to complications during childbirth, requiring careful management by medical professionals.
  • Genetic Disorders: Mirror twins, like all identical twins, share the same genetic material. If there are genetic predispositions or mutations, both twins may be at risk of inheriting certain genetic disorders.

Difference Between Mirror Twins and Identical Twins

Identical twins are monozygotic, which means a single fertilised egg splits into two and forms two embryos that share the same genetic material. Identical twins are formed when the egg splits into two between day 2 and day 8, while mirror twins are formed when the egg splits late, between day 9 and day 12 causing the twins to mirror each other. If the egg splits after 12 days, it results in conjoined twins, where the twins are not completely separated from each other and may even share an organ.

Mirror twins are identical twins, and their characteristics mirror each other. All mirror twins are identical twins, but all identical twins may not be mirror image twins.


1. Can Mirror Twins Feel the Pain of Each Other’s?

No scientific evidence supports the idea that mirror twins can feel each other’s physical pain. While they may share a unique connection, sensations of pain are individual experiences.

2. Do Mirror Image Twins Share Identical Fingerprints?

Despite sharing nearly identical genetic material, mirror twins do not have identical fingerprints. Fingerprints are influenced by both genetic and environmental factors, leading to individualized patterns.

3. Who Are the Famous Mirror Twins?

Here are some of the famous mirror twins:

  • Mary-Kate and Ashley Olsen
  • Rumi and Sir Carter
  • Tia Mowry and Tamera Mowry
  • Deidre Hall and Andrea Hall-Gengler
  • Charlotte Ronson and Samantha Ronson

Mirror twins are a fascinating type of identical twins. Not every set of mirror-image twins will be opposite-handed or will have moles on the opposite sides. This is because the degree of mirror imaging differs for every set of twins.


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2. Wang. E, Xu. X, Dagum. A; Mirror-image Trigger Thumb in Dichorionic Identical Twins (Orthopedics); SLACK Journals; https://journals.healio.com/doi/10.3928/01477447-20120525-48; May 2012

3. Hughes. T, Pinkerton. S, Seow. W, et. al.; The teeth and faces of twins: providing insights into dentofacial development and oral health for practising oral health professionals (Australian Dental Journal); Wiley Online Library; https://onlinelibrary.wiley.com/doi/10.1111/adj.12101; October 2013

4. About twins; Twins Research Australia; https://twins.org.au/twins-and-families/about-twins/

5. Golbin. A, Golbin. Y, Keith. L, Keith. D; Mirror Imaging in Twins: Biological Polarization – an Evolving Hypothesis; Cambridge University Press; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/7939D57B35DD70CC0D6FE2B5919B5D1A/S0001566000003238a.pdf, July 1993

6. Identical twins: One right, one left; Penn State; https://sites.psu.edu/clarep/2016/10/21/identical-twins-one-right-one-left/

7. Situs inversus totalis; Genetic and Rare Diseases Information Center; https://rarediseases.info.nih.gov/diseases/4883/situs-inversus

Also Read:

Fraternal Twins
Vanishing Twin Syndrome
Surprising Facts about Twins
What Is Twin Telepathy and Does It Exist?

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