Fun Facts

Odds of Having Twins and Higher:

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.

Fertility Drugs and Other Methods:
Chance of Multiples While on Clomid:
Twins - 1 in 10
Triplets - 1 in 200
Quadruplets - 1 in 333
Quintuplets - 1 in 1000
Overall you have a 1 in 6.5 chance of conceiving multiples while taking Clomid.

Zygosity (Identical vs Fraternal) and Sex of Multiples:

Twins:
Of the 1/3 of twin births that are 2 boys, 1/6 are identical and 1/6 are fraternal
Of the 1/3 of twin births that are 2 girls, 1/6 are identical and 1/6 are fraternal

Triplets:

Naturally you will find the most common to be 2 identical and 1 fraternal, but with the use of fertility methods, it's probably more common, or equally as common, to see all fraternals now.

Quads:

I have found in my own records the most common is: all fraternal (most due to fertility drugs), then 2 identical and 2 fraternal (70 sets), mostly tied for 3rd place are 2 sets of identical (15 sets) and 3 identical and 1 fraternal (16 sets), then finally all identical (29 to 37 sets).
The reason I say all identical is more rare that 2 sets of identical and 3 identical/1 fraternal is due to the fact that their are many sets I don't know the zygosity of, and that all identicals usually get more media attention and are easier to hear about.

Quints:

The most common identical pairing, is 2 identical and 3 fraternal. On my World Quints page, 12 sets have 2 identicals in them. Only one set has 2 sets of identical and a fraternal, and no living sets have more than that, the rest are all fraternal - not counting the surviving Dionne's of course).

Your percentage of having females is higher with each multiple birth:
48.4% female in single births
49.2% female in twin births
50.5% female in triplet births

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.

This info is compiled on http://multiplemommies.tripod.com/id4.html and was 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.