Facts About Multiples
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Multiple Birth Odds
How Multiples Are Formed ~ Twinning Rates ~
Various Statistics ~ Conjoined Twins Stats ~
Risks Overall Multiple Birth Rates: In 2000, 2.9% of all births in the USA were twins. Australia: 1
in 72 In Canada approximately 4200 sets of twins are born each year. These statistics are not infallible. The use of fertility treatments will cause the number of multiple births to become higher, so they could be as high as 1 in 38 (as in the USA) with the use of fertility drugs, to about 1 in 90 without (for all types of twins). Of those with higher order multiples (triplets and above), about 79% will be triplets, 14% will be quadruplets, 6% will be quintuplets and 1% will have sextuplets or more. There are over 125 million twins in the world.
Overall Twin Rates: USA: 1 per 30.1
(using statistics of births in 2001) In Sweden in the 1970s about 1800 twins were born, and in 1990s it was close to 3000. 1 in 50 people is a fraternal twin in the USA, and 1 in 150 is an identical twin. 1/3 of all twins born in the US are identical, but in Japan the figure is 2/3. Of all twins born, 30% will be identical and 70% will be fraternal. Since 1989 there have been an average of 56,136 sets of twins born each year in the US. Fraternal Twin Rates: World: 1 in 42.85 Identical Twin Rates: 1 in 285 (this figure seems to be universal and random) Conjoined Twins: 1 in 50,000 Your percentage of having females is higher with each multiple birth: 48.4% female in single births
Triplets: White Americans: 1 in 8100 chance I believe these stats were for spontaneous conception of triplets. Other stats I have recently seen which include spontaneous and fertility treatments: US Triplet Rate
1989: 1 in 1445 US Triplet and Higher Rate 2001: 1 per 539 In Sweden, triplets were born at a rate of about 10 per year in the 60s and 70s, which rose to 20 per year in the 80s and up to 60 in 1993. It then fell again to about 20 per year in the later 90s. Switzerland: 1 in 3247 live births The rate of identical triplets has stayed the same, since obviously fertility drugs do not affect their rate of conception. But the overall triplet rate has risen, making identical triplets rarer today than they were 25 or 50 years ago. Since 1989 there have been an average of 1802 sets of triplets born each year in the US (around 150 of the sets would be all identical triplets).
Quadruplet Rates: Medical literature reported 46 sets of quadruplets worldwide in the first 50 years of this century. In 1994 alone, at least 79 sets of quadruplets were born in the United States. In China's population of 1.2 billion, there are 32 sets of quadruplets (1999?), including five sets in Hong Kong and Taiwan. In 1996, eight sets were born in China, of which five survived. Switzerland: 1 in 81,186 live births 474 sets of quadruplets have been born without fertility methods (out of the 3112 sets of quadruplets counted Jan 06). 15.23% of all quads are spontaneous. Since 1989 there have been an average of 102 sets of quads born each year in the US. 7.74% of all quads will have some identical children. (Jan 06) Of those quads with identicals 12.86% will be from IVF. (Of all quads, 0.99% will be from IVF and have some identicals in them) (Jan 06)
Quintuplet Rates: Since 1989 there have been an average of 12 sets of quintuplets and higher born in the US each year. There are approximately 202 sets (give or take) of quintuplets that have been born in the USA. (as of Aug 2004) 109 of 577 sets on my World Quads list were reported to be spontaneous, a rate of 18.89%. Most of the spontaneous sets occurred before the advent of fertility methods. Since 1965, only 20 sets have been spontaneous. (Dec 04) 4.68% of quints will have some identical children in them. (Dec 04)
Sextuplet Rates: Since 1989 there have been an average of 1.125 sets of sextuplets born each year in the USA. 32 out of 147 sets were reportedly spontaneously conceived, which is 21.77% of all sextuplet births (The number is high because of the high number of births I found of sextuplets in early centuries. Since fertility drugs, there have been only 6 sets that were reported as spontaneously conceived. (About 4% worth) (Dec 04) Approximately 2.72% of sextuplets will have some identical babies in them, most often 2 identical and 4 fraternal. (Dec 04)
Hellin's Law: Hellin's Law states that before the advent of fertility methods, the natural occurrence of multiples would be as follows: Twins - 1 in 86 live births
Statistics of natural births of quadruplets and higher multiples have worked out to be somewhat lower than this for quads and higher. A Russian study of 13 million births, discovered twins occurred naturally once in 88 births; triplets, once in 7910; and quadruplets, once in 371,126, which is twice as common as Hellin's Law hypothesizes. These numbers have lowered to 1 in 38 for twins with fertility methods, as well as lowering the numbers for all other multiples. It is estimated that 60% of triplets are from fertility treatments, 90% of quadruplets are from fertility treatments, and 99% of quintuplets are due to fertility treatments. One in 495,306 people is a quadruplet. One in 24.7 to 27.6 million people is an identical quadruplet. One in 1,773,950 people is a quintuplet. One in 6,634,287 people in a sextuplet. One in 19,428,984 people is a septuplet.
More Than One Set?: If you have had fraternal twins already, your chance of having another set quadruples. This is because most women who conceive fraternals (without fertility drugs) show a pattern of releasing more than one egg per cycle. This is the breakdown on how common 2 sets of twins are in various zygosity combinations. 2 sets of fraternal twins - 1 in 3000 According to a British paper, the chance of having three sets of twins (any zygosity), is about 1 in 500,000.
If You Are A Twin (Or Have Twins In Your Family): If you are a fraternal twin, you have a 1 in 17 chance of having twins. If you are identical, it doesn't affect your chances, and they remain from 1 in anywhere from 38 - 90, depending on if fertility drugs are used or not. If your mother is a fraternal twin, you may have a higher than average chance of twins. If you father is a twin and you are a female, it may slightly increase your chances. If your husband is a twin or has twins in his family, it doesn't affect your chances of having twins. If you have a parent that is an identical twin, your chance of having twins yourself are the same as anyone else. There is some belief that identical twinning may also have a genetic factor, but there is no concrete evidence of this. US Multiple Births Per Year: These stats are for individual babies and sets and I've noted what numbers are sets of multiples. The sets may be off because the stats only counted surviving babies, and the quint stats also included higher multiple sets born. Triplet, quadruplet, and quint+ births were sometimes counted as one category, and I've added them if I can't find the breakdowns of specific sets. Sextuplet and septuplet births are included in the Quints and Higher stats. Any column without listings I don't have statistics for yet. While it looks like a huge increase between 1916 and later years, the birth rate per 1000 was steady at around 10. Births in general were down in these years.
Since 1980 there
have been an average of 48,810 sets of twins born each year in the
US. *Note - The figures in this column count triplets, quads, quints and higher births all together and are individual babies born, not sets. The above stats are from the National Center for Health Statistics and the National Health Information Center. Note: These statistics were collected from many resources, including government agencies of the various listed countries, over 800 newspapers, books and scientific journal articles. Because some of the sources of the information are research statistics they are liable to be different for different researchers depending on the size of the test group and many other factors, therefore it's not uncommon for some of the numbers to vary depending on the source of the information.
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