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20 Amazing Facts About Twins

October 12th, 2010


By Kitty Holman

Twins have fascinated mankind for thousands of years. Even today, when having five or even six little ones in a go isn't impossible, twins still draw attention, speculation and intrigue. Yet many still don't know all that much about what causes the phenomenon or what it really means to be a twin. Whether you're in nursing school or just like learning about the medical field, here are some interesting, amazing and fun facts about twins you might like to know.

  1. A whopping 22% of twins are left handed. Amongst the general population, the number shrinks to 10%. Handedness isn't always a clearly genetic trait, and the factors that go into it can be quite complex. In fact, scientists are not even entirely sure how or why so many twins are left-handed – just that it very likely has to do with a connection between a genetic predisposition for twinning and a genetic bias for left handedness. Why are the two connected? We still don't know.
  2. Rates of twin births vary by location. Certain areas of the world and our own nation have much higher rates of twin births than other places. For instance, if you live in Massachusetts, New Jersey or Connecticut, the twinning rate is 25% higher than the general populace. On the flip side, Hawaii and New Mexico have a twin birth rate 30% lower than that of the national average. Scientists believe that this propensity for multiple births is the product of multiple factors involving fertility drugs, heredity, food choices and age.
  3. While most people are only familiar with identical and fraternal twins, there are actually 7 different types of twins. They are: identical, fraternal, half-identical, mirror image twins, mixed chromosome twins, superfecundation, and superfetation. Those other than identical and fraternal can be quite rare.
  4. Twins do not have to be born on the same date. In fact, they can be born surprisingly far apart. The longest recorded gap between twin births is 85 days. How does this happen? The simplest explanation comes when one twin is born just before midnight and the other after. In cases where there is a longer gap, it's often because one twin is born early due to complications, while the other is left in the womb to further develop. This is much safer for the second baby and can help improve survival rates.
  5. Twins do not have to have the same father. While we often think of twins as having the same mother and father, it's possible for a woman to give birth to two children on the same day who don't share a father. This phenomenon is called heteropaternal superfecundation. It happens when a woman releases multiple eggs, each fertilized by sperm from separate instances of sexual intercourse. It's uncommon, but genetic testing has shown that it is possible.
  6. Identical twins have different fingerprints. Some people might think that identical twins are the same right down to those whorls and swirls on their fingerprints, but while identical twins share most of their genetic material, identical fingerprints aren't among them. While the fingerprints may be very similar, on close examination it is possible to tell them apart – much like the twins themselves.
  7. About 25% of identical twins are called mirror image twins. This means that they are, in fact, identical, but only in the way that your reflection in a mirror is an identical image of you. For example, if one twin has a mole under her right eye, the other will have it under her left eye. Scientists think this is due to the fertilized egg splitting later than the norm for identical twins, around nine to twelve days after fertilization.
  8. Identical twins have almost identical brainwave patterns. The notion that twins think alike just might be true. Research on identical twins shows that they have almost perfectly matching brainwave patterns. Some think this could explain twins' abilities to know what the other is thinking and feeling.
  9. Twins can celebrate their twinning in Twinsberg, Ohio. If you or your children are twins, you can head to this city in Ohio to celebrate the Twins Days Festival. You'll be amid a sea of look-alikes, with twins, triplets and multiples from all over the nation converging on this town to celebrate being a twin.
  10. Twins often develop their own language. This phenomena is called idioglossia. It's something that has fascinated people about twins for years, but it's really a relatively simple and easily understandable process. It happens when one twin models the disordered or incorrect speech of the other, leading to both twins using the same grammatical or speech sound errors. It sounds like a foreign language, but is really just a normal part of cognitive development.
  11. Identical twins can be of different sexes. It might sound strange to stay that identical twins can be different when it comes to gender, but technically speaking it is possible. It happens when the egg splitting process doesn't happen quite as it should, resulting in twins that display genetic abnormalities like Klinefelter's syndrome. This means one twin might have the right correlation of XX or XY while the other has XXY.
  12. Twins share DNA, but it is not identical. While identical twins come from the same sperm and egg, their DNA isn't necessarily identical, according to new research. Scientists used to think differences in twins were due to environmental factors; they now know that isn't the only force causing variations. Genetic studies have demonstrated that there are certain points where twins will veer away from one another, with one carrying different or multiple copies of the same gene.
  13. Certain diets may increase your chances of having twins. What a woman eats can help increase her chances of having twins, or so researchers think. While genetics obviously plays a big role, diet can also influence this phenomenon. Researchers have found that women who eat dairy and animal products are much more likely to have twins than those that don't. This is likely due to a protein called IGF that increases the sensitivity of the ovaries to hormones that cause ovulation.
  14. Fraternal twinning is genetically predisposed. Identical twinning is random. Fraternal twinning is the result of a woman releasing multiple eggs at the same time, and is largely the result of a genetic predisposition to release this extras. Identical twins, however, are the result of a random split of a single egg, something which cannot be genetically predisposed. In recent years, the number of fraternal twins has risen in response to fertility treatments, while the number of identical twin births has stayed the same.
  15. Fraternal twins can have vastly different skin colors. This is an incredibly rare phenomenon (the odds of such births are 1 in a million according to some experts), but it does happen. When parents of mixed or different races have twins, they can have quite different skin colors upon birth. A number of cases have made the news in recent years and have fascinated the public at large. Because fraternal twins don't share identical genetic material, one may inherit the genes for one skin color, the other another. The parents provide potential coding for either.
  16. Twins can have different gestational age. When it comes to fraternal twins, fertilization doesn't always have to happen at the same time. Fraternal twinning is the product of releasing two eggs within the same cycle, and the eggs are not necessarily released on the same day. One egg may be fertilized days (even weeks) before the other, leading to a difference – however slight – in the age and development of the twins.
  17. 27 lbs and 12oz is the heaviest combined birth weight of any set of twins. if you think it would be rough to carry around and deliver one 14-pound baby, then imagine doing it with two. That's just what happened in this case, the largest twin birth on record. Of course, it doesn't hold a candle to the largest singleton birth weight of 23 pounds.
  18. Twins separated at birth and reunited are often found to be eerily similar in personality and interests. The studies that discovered this fact, however, have widely been condemned as some of the cruelest and morally repugnant in medical history. During the 60's and 70's, identical twins were separated at birth in an attempt to determine whether it was nature or nurture that determined their personalities. However unethical, the study demonstrated that a great deal of who we are comes from our genes; many of the twins bore uncanny similarities in personality and preferences despite spending decades apart.
  19. Scientists believe that the number of twin conceptions greatly outnumbers the number of twin births. Twin conceptions are much more common than many people realize. Of course, these conceptions do not always result in the birth of two healthy babies. Very often, one of the fertilized eggs or embryos will be reabsorbed into the mother's womb in a phenomenon called "vanishing twin syndrome."
  20. The incidence of twin types and genders are oddly symmetrical. These facts about twinning are sure to leave you in awe. One third of all twins born are identical, one third are same sex fraternal and one third are male/female fraternal. Of the identical twins, half are male/male and half are female/female. Of the same sex fraternal, half are male/male and half are female/female.


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