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This info has been gathered from Elizabeth Noble's book Having Twins, and the book Twins
and What They Tell Us About Who We Are, The Vancouver Province, Kay Cassil's book Twins: Nature's Amazing Mystery as well
as research on the net.
Twin Basics
Odds of Having Twins and Higher:
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Fraternal Twin Rates:
JAPAN: 6 per 1000 births are fraternal twins (1 in 166), 3.5 per 1000 are identical twins
NIGERIA: 45 per
1000 (1 in 22)
USA: 11 per 1000 (1 in 90) (I suspect this stat is quite old)
World: 22.8 per 1000
Identical
Twin Rates:
3.5 per 1000 (1 in 285) (this figure seems to be universal and random)
Conjoined Twins:
1 in 50,000
Overall
Twin Rates:
Black Americans: 30.0 per 1000 (1997), 32.1 per 1000 (1999)
Hispanic
Americans: 19.5 per 1000 (1997), 20.1 per 1000 (1999)
White Americans: 28.8 per 1000 (1997), 31.5 per 1000 (1999)
Americans:
28.9 per 1000 (1997)
Japanese: 1 in 150
Chinese: 1 in 250
Mixed Asian: 1 in 125
Nigerian: 1 in 22
Norway,
Denmark, Netherlands: 1 in 49
England: 1 in 76
Overall Multiples Rates:
England/Wales: 13.22 per 1000 (1994)
Scotland:
12.99 per 1000 (1994)
Northern Ireland: 12.21 per 1000 (1994)
United Kingdom: 13.17 per 1000 (1994)
Australia: 1/72
Belgium:
1/55
Canada: 1/85
Finland: 1/64
Japan: 1/120
UK: 1/70
US: 1/30
Sweden: 1/70
Switzerland: 1/80
These
statistics are not infallible. The use of fertility treatments will cause the
number of twin births to become higher,
so they could be as high as 1 in 38 with the use
of fertility drugs, to about 1 in 68 without (for all types of twins).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.
Triplets:
White Americans: 1 in 8100 chance
Black Americans: 1 in 9800
chance
It is believed these stats were for spontaneous conception of triplets. Other stats I have
recently seen which
include spontaneous and fertility treatments:
Triplet Rate 1989: 69.2 per 100, 000 (1 in 1445)
Triplet Rate 1995: 127.5
per 100,000 (1 in 784)
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. If a woman has one set of identicals, her chance
of having another set of identical twins
is 1 in 70,000 or less. About 1 in 3000 women
will have two sets of twins (didn't state what zygosity). 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, it doesn't
affect your chances, as fraternal
twinning is apparently carried down the maternal line. 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 chances of having twins yourself are the same as anyone else.
Note: Please note that these statistics were collected
from many resources, and are most
likely not completely accurate. I am aware that many of the numbers contradict
each
other as well. I am always trying to find accurate information, and will update when I can.
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