Fun Facts About Gemellology:

  • The scientific study of twins is known as "gemellology." The word twin is probably derived from an ancient German word twine, which means 'two together.' 
  • Worldwide there are at least 125 million living multiples.
  • The incidence of twin types and genders are oddly symmetrical. 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.
  • Did you know that up to 22 percent of twins are left-handed. In the non-twin population the number is just under 10 percent.
  • Identical twins exhibit almost identical brain wave patterns.
  • Twins and multiples have been know to develop their own 'language' that only they understand. This is known as cryptophasia or idioglossia.
  • The average time between the delivery of the first and second twin is 17 minutes
  • Australia produced the world's first test-tube twins in June 1981. They are also know for producing the world's first triplets and quadruplets.
  • Nigeria has the highest rates of multiples with more identical twins than fraternal, while China has one of the lowest with multiple births occurring one in 300 births.
  • The largest surviving complete set is of septuplets (in US). Three complete sets of sextuplets survive in the UK (6 girls in 1983, 3 boys and 3 girls in 1986 and 1 boy and 5 girls in 1993).
  • Scientists believe that the number of twin conceptions greatly outnumbers the number of twin births, some say that as many as one in eight births began with twins, while in only one in 70 births produce twins. One author claims that "80% of twin pregnancies result in the loss of one or both babies," though other sources cite this number at about 30%. Of the 133 million people born worldwide in 2000, an estimated seven million should have been twins.
  • Incredible fact:  In 1853, a peasant named Kirilow was presented to the empress of Russia as he had been married twice and his wives gave birth to 72 children including 4 sets of quads, 8 sets of triplets and 8 sets of twins!
  • The world's oldest twins were Eli Shadrack and John Meshak Phipps born on Feb 14 1803 in Viginia and died at the ages of 108 and 113 respectively. The chances of identical twins surpassing the age of 100 is 1 in 700 million.
  • William Shakespeare was the father of boy/girl twins, Hamnet & Judith and he also wrote about twins in The Comedy of Errors and Twelfth Night.
  • A 1983 study revealed that a mother of six-month-old-triplets expends an average of 197.5 hours per week (out of a possible 168) between herself and paid/volunteer assistance, on the care of her children and home. This did not include a time allowance for mother to bathe, dress, sleep, eat, relax or talk with partner!

Influences on Twinning Rate - What are your chances of having twins?

  • Maternal family history of twins, mother's age, maternal height and weight, number of previous pregnancies, race as well as infertility treatments such as IVF are determining factors in the incidence of fraternal multiples.
  • If the mother herself is a fraternal twin, the chances of having twins increases about four-fold.
  • The rate for identical, or monozygotic, multiples is random and universal; it's the same in all populations regardless of race, heredity or other factors, and it has remained constant over time. The chances of having identical twins is about 1 in 285 or 3.5 per 1000 maternities.
  • The Yoruba tribe of Nigeria have the highest twinning rate in the entire world (3 sets of twins in every 19 births). The Nigerian people attribute it to their population's consumption of a specific type of yam. Scientists have discovered that these colourful vegetables contain a high level of a substance that is similar to the hormone oestrogen, which could bring on multiple ovulation. Chief Adeyemisays “It's an honour to be so-called Baba or Iya Ibeji [Father or mother of twins] because they are a special breed from God.”
  • The time of year and the number of daylight hours may also have an impact on multiple births. Scientists speculate that this is probably due to the longer length of daylight in July, which allows for a higher secretion of the Follicle Stimulating Hormone in wome.
  • There is an intriguing new concept in the field of reproductive medicine about a possible connection between diet and twinning. Preliminary results in a recent report indicate that women who consume dairy products are five times more likely to have twins than those who don't, possibly because of synthetic growth hormones added to milk that generate a protein called IGF (the use of growth hormones is banned in Europe since it's introduction in the 1990's but has been suggested as part of the dramatic increase in twins in the USA).


  • Multiple births in UK has been on the rise: birth of twins has risen almost 50% from 1984 – 2004 (latest data).
  • Around 98.5% of all multiple births in the UK are twins and more than 9,000 sets of twins are born in the UK each year. In 2004, there were 10,548 multiple births.
  • In 2004, about 1 in 34 babies was born a twin or a triplet in the UK (1980 1 in 52)
  • Incidents of quadruplets is one in 142,000 births (In 2004, there were 5 sets born)
  • Incidence of quintuplets and sextuplets is very rare in the UK (Most recently, in 2002, there were 2 sets of quints born and in 1993 1 set of sextuplets born).

Genetics & Types of Twins/Triplets

  • Maternal family history of twins, mother's age, maternal height and weight, number of previous pregnancies, race as well as infertility treatments such as IVF are determining factors in the incidence of fraternal multiples. Genetic factors do not have much, if any, affect on the incidence of identical twins. Identical twins do not run in families.
  • Fraternal (dizygotic/trizygotic) twins/triplets are the result of two/three fertilized eggs, each fertilized by different sperm. That mean they share only 50% of their DNA, much like all other singleton siblings. They can be the same or opposite sexes. Fraternal twinning does not necessarily skip a generation. Interestingly, they can as dissimilar as some singleton siblings OR they can look like identical twins!
  • Identical (monozygotic) twins/triplets are the result of a single egg splitting after conception. These twins will share 100% of their DNA. They are the same sex, have the same blood types, hair and eye color, hand and footprints and chromosomes, yet have different teeth marks and fingerprints. Environmental influences can determine that characteristics such as height, weight, ears, nose, lips are somewhat different. Some monozygotic multiples are told they are fraternal (dizygotic) - only DNA testing provides conclusive results.
  • Mirror Image twins account for about 25% of identical twins. Their hair falls in opposite directions, they have mirror image fingerprints and if one is right handed, the other is left handed. There is no specific test for determining if twins are mirror-image, however. The determination is made by observation only, and the twins must be monozygotic (identical).
  • Conjoined twins ("Siamese") are those that are joined at birth and are extrememly rare occuring in as few as one in 200,000 births. They are always identical as they derive from one egg that for unknown reasons has failed to divide fully into identical twins. The term Siamese twins was coined as a reference to Eng and Chang Bunker who were born in Siam in 1811 (now Thailand). The term 'Siamese twins' is no longer considered appropriate.
  • Polar Body or half identical twins, occur when one egg splits in two before fertilization. Each half is then fertilized by a separate sperm. These twins share 75% of their DNA as they share the same DNA from one egg and different DNA from each sperm.
  • Twins of Two occur when two eggs are released by the ovaries and each egg is fertilized by a different father. These fraternal twins are genetically half-siblings and share 25% of their DNA.

Health & Costs

  • Almost half of all twins are born prematurely and/or have low birth-weight. Full term for twins is considered 37 weeks and low birth weight below 5.5lbs.. 
  • Over 90% of triplet, quadruplet and quintuplet babies are born prematurely and/or have low birth-weight.
  • Older mothers traditionally have a higher chance of delivering fraternal twins, with the odds increasing when the mother is 35 years or older and dramatically increasing for the over 45’s.
  • The average duration of a regular pregnancy is 40 weeks. In a twin pregnancy, the average is 37 weeks, for triplets 34 and quadruplets 32 weeks.
  • The average birth weight for singletons is 7 lbs 7 oz. Average birth weight of twins is 5 lbs 5 oz, for triplets 4lbs and quads 3lbs. A difference in birth weight between multiples is not unusual.
  • Recent articles in the press have reported that the cost of each birth in a twin and triplet delivery was 2 to 3 times that of a birth in a singleton delivery.

From: Twins UK

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