Things You've Always Wondered About Twins

Are you fascinated by twins? They've been the subject of myth and mystery and a source of curiosity to many. Even those who know twins or have them in the family may have some questions about them. You may have given some thought to what causes twins or why they happen, but did you ever wonder if some of the rumors are true? Explore the mysteries of these things that you've always wondered about twins. 


Do Twins Have the Same Fingerprints?

Identical twin baby girls

Rebecca Emery / Photodisc / Getty Images

Twins have a lot in common. They usually share a birthday, and identical twins even share the same DNA. But what about fingerprints? Are they alike even down to this finest of physical details?

No; twins do not have the same fingerprints. Research has found that twin fingerprints are more likely to share the same pattern-type than non-twin fingerprints, but they are distinguishable from one another.


Can Different Sexes Be Identical Twins?

Boy and girl twins
Eclisse Creazioni Art & Photography / Getty Images

Twins assigned different sexes at birth are always dizygotic (fraternal). Dizygotic twins form from two separate eggs that are fertilized by two separate sperm. They may be different sexes or the same sex. Monozygotic, or identical, twins are always assigned the same sex at birth.

While fraternal twins share similarities with each other, those similarities are comparable to siblings from separate pregnancies. So although they may look very much alike (as siblings often do), fraternal twins are not identical.


Can Twins Read Each Other's Minds?

It's true that multiples can share a special connection that goes beyond that of ordinary siblings. Sometimes they will say or do the same thing at the same time. Some twins relate incredible stories of coincidence, where they think the same thoughts or sense each other's feelings. 

Older studies on twin relationships have indicated that twins may share a stronger bond than non-twin siblings. However, more recent research has found no difference between twin and non-twin sibling relationships in terms of how they behaved toward one another. 

While there may be anecdotal evidence for a strong bond between multiples, there is not sufficient research to conclude that twin telepathy exists.


Can There Be a Hidden Twin?

Twin ultrasound picture seven weeks

Pamela Prindle Fierro

In times past, twins were often a surprise to their parents. Instead of one baby, two arrived! But now that ultrasound allows a sneak peek into the womb, there are rarely instances of a hidden twin.

Despite the clarity of modern technology, multiples still manage to pull a few surprises and remain hidden from view during a portion of pregnancy. This is more likely to happen if your ultrasound was done before 20 weeks, you didn't have an ultrasound, or if you have not received prenatal care.


Do Twins Have Their Own Language?

Twins whispering

Floresco Productions / Getty Images

It is estimated that up to 50% of twins may use an autonomous language, known as cryptophasia. According to the American Speech-Hearing-Language Association, what appears to be a secret language between twins may actually be a delay in phonology (rules used to put speech sounds together).

Some twins use a secret language with one another and communicate effectively with others, like parents, so it's not always an indicator of a problem. However, secret twin language may be a risk factor for speech and language delays.

If you are unsure whether your twins' secret language could indicate a speech delay, contact a speech-language therapist for an evaluation. They will be able to help you determine if your children's speech patterns are developmentally appropriate.


If Identical Twins Have the Same DNA, Why Aren't They Exactly Alike?

Twins sitting on chairs, wearing different styles
James Woodson / Getty Images

Anyone who knows a set of identical twins knows that they are alike in many ways, but also very unique individuals. Why is that? 

While twins often look very similar and may even share some of the same tastes and interests, they're also very different. Identical twins form from a single egg and sperm combination and share the same genes, but environmental factors can influence differences in in twins' characters.


Can Twins Have Different Birthdays?

Twins celebrating birthday with cake
Getty Images / Photodisc

Twins, by definition, are two offspring born together, right? Yet, some twins blow out their candles on different days. Often, twins are born minutes apart—sometimes that interval just happens to be as a day or year changes over. But, other times, the span between each twin's birth can be even greater.

When a pregnancy has a complication, such as preterm birth, a practice called delayed interval delivery may be used to stop labor after the birth of the first baby, allowing the other time to develop more fully before they are born. This is very rare, but there have been case reports of delayed interval delivery of a month or more between births.


Do Twins Run in Families?

Two sets of twins
Jessica Holden Photography / Getty Images

Monozygotic twins occur when a single egg is fertilized by a single sperm. The zygote then splits in early pregnancy, forming identical twins. Monozygotic twinning is not believed to be related to genes, although there are some families with an unusual number of identical twins, so it is possible that genes may play a role.

Dizygotic twins, on the other hand, form when two eggs are fertilized by two sperm. In order for this to occur, a person has to release more than one egg during a cycle. This is known as hyperovulation, and it may run in some families. If your parent or sibling had dizygotic twins, you are twice as likely to have twins yourself.


Are Irish Twins Really Twins?

"Irish twins"
Moment / Getty Images

"Irish twins" are not really twins. The term refers to siblings who are born within 12 months of one another. "Irish twins" do not share the same gestational period, but are simply siblings who are very close in age.

This is a slang term that stereotypes Irish culture. So, even if you intend to use it affectionately, it's better to avoid it.


Can Twins Have Different Fathers?

By definition, twins have the same gestational parent. But it is possible for some twins to have different non-gestational parents. Since monozygotic twins form from the separation of one egg that is fertilized by a single sperm, they can only have one non-gestational parent.

Dizygotic twins, on the other hand, are formed from two eggs fertilized by two different sperm. So, there is a chance that fraternal twins could have different non-gestational parents. Known as heteropaternal superfecundation, resulting twins are genetically equivalent to half-siblings. The frequency is unknown but presumed to be rare. It is also likely underestimated.


Do Twins Skip a Generation?

Twins riding on parents' shoulders

Cultura RM / JLPH / Getty Images

A common myth is that twins skip a generation. Genes, though, don't skip generations. The myth may have come about because sometimes the person with the twinning gene does not ovulate, so they don't produce multiple eggs resulting in twins. But they may pass the gene along to their own children. If those children eventually ovulate, they may go on to have twins, causing the illusion that twins skip a generation.


What Causes Identical Twinning?

Monozygotic twins occur in three to four out of every 1,000 births. There are not many known factors that increase the chances of identical multiples. The occurrence of identical twins that are conceived without assistance is believed to be random.

Ovarian stimulation and other assisted reproductive techniques (ART) may increase the rate of monozygotic twins by as much as 60%.

10 Sources
Verywell Family 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.
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