Facts About Multiples
An Encyclopedia of Multiple Birth Records

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Hormone Therapy (Clomid, Pergonal, HcG etc):

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.

Chance of Multiples on HCG:

Twins - 20%
Triplets - 5%
Quadruplets - 2%
Quintuplets - 1%
Sextuplets - 0.5%

You have a 20% chance of multiples while on Pergonal.

Any quints born before July 1965 will be spontaneously conceived.

Assisted Reproductive Technology:

IVF:

About 25-30% of IVF pregnancies are multiple births, most of these twins.

1 in 4 IVF births results in twins, 1 in 22 IVF births results in triplets.

In a 1998 study of 2906 IVF multiple births, the breakdown was as follows:

Twins - 80.87%
Triplets - 17.48%
Quadruplets and Higher - 1.65%

In Canada, approximately 23% of IVF live birth confinements result in multiple births.

Twins born before June 1981, triplets born before June 1983, quads born before January 1984 and quints born before April 1985 will not be from IVF.

Out of all quadruplets born, 0.59% will have some identicals and be IVF sets as well. There are theories that the handling of the egg in ART technologies thins the protective covering of the egg and making it easier for the embryo to divide into twins. The other way identicals can happen is if the mother conceives identical twins spontaneously and also has IVF that results in a conception at the same time.

GIFT:

About 35% will result in multiples.

ZIFT:

About 35% will result in multiples.

All Fertility Methods:

In 1996, 38% of all fertility treatments resulted in multiple births.

A Canadian study at McMaster University determined that approximately 34.7% of live births in Canada are from fertility treatments are of twins, while 1.7% of fertility treatment births resulted in triplets and quadruplets.

In a 1997 British study it was found that 25-30% of multiple births occur naturally and the remaining 70-75% are a result of fertility treatments.

Oddly enough, monozygotic twinning (identical twinning) is 2 to 3 times higher in IVF and fertility drug multiples than spontaneously occuring identicals. Some scientists have theorized that because the egg is handled so much in IVF, that the protective covering is thinned out during the process, which leads to identical twinning occuring more easily.

Approximately 2% of singletons, 35% of twins, and 77% of higher order multiples are due to fertility treatments.

Twinning should occur naturally in 8% of all births.

There have been 3 sets of quadruplets conceived where some of the babies were conceived by IVF, and the others natural conception at the same time.

There have been 21 sets of IVF quads born that have some identical babies.

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Here is a break down of how multiples were conceived from a 1989 and 1994 study of multiples:

Twins:

Roughly 1/3 of all twins are identical; 2/3 of all twins are fraternal (33% identical, 67% fraternal).

The following rates are just approximations:

1/3 of twin births are b/b. Of these boy/boy pairs, 1/3 are identical and 2/3 are fraternal. This means that 1/9 of all twins are identical boys and 2/9 are fraternal boys.
1/3 of twin births are g/g. Of these girl/girl pairs, 1/3 of them are identicals and 2/3 are fraternal. This means that 1/9 of twins are identical girls and 2/9 are fraternal girls.
1/3 of twin births are b/g. Of these boy/girl pairs, 0/3 (none) are identical and 3/3 (all) are fraternal. This means that 3/9 of all twins are fraternal b/g.

The fraternal rate is likely much higher now because of fertility treatments (probably 75% or more are fraternal now). MOST Online found that only 56% of their surveyed twin families had spontaneous conceptions.

Triplets:

Spontaneously you will find the most common to be 2 identical and 1 fraternal, but with the use of fertility methods, it's more common to see all fraternals now. The spontaneous rates are approximately:

1. Two identical/1 fraternal - 70%
2. All fraternal - 30%
3. All identical - 10%

MOST Online's survey of 1119 triplet families (spontaneous and assisted conceptions) found the following zygosity breakdown:

1. All fraternal - 82%
2. Two identical/one fraternal - 10%
3. All identical - 3%

5% of births were unknown zygosity.

MOST Online found that only 16% of their surveyed families had spontaneous conception of triplets.

Conceptions of identicals are lower now than they were in the past because fertility methods have increased the number of fraternal conceptions of multiples.

Quads:

According to my stats, the most common zygosity of quadruplets is (this is including fertility treatments):

1. All fraternal - 92%
2. Mixed id/ft - 7.74%

MOST Online's survey of 178 quadruplet families (spontaneous and assisted conceptions) found the following zygosity breakdown:

1. All fraternal - 87%
2. Mixed identical/fraternal - 8%
3. All identical - 0.6%

4.4% were unknown

MOST had a smaller group than my stats have available to me, but they also had direct info from the families, whereas my list surely has sets that have some identicals in them and they aren't specified.

MOST Online found 5% of their surveyed families had spontaneous conception of quads.

The rough odds of having all identical quadruplets is between 1 in 11.5 million to 1 in 13.9 million, based on an estimated global population of 6.5 billion and between 50 and 58 sets of identical quads that have been born in the world (and are known about).

Quints:

Almost all quints are fraternal. The most common identical pairing is 2 identical and 3 fraternal. These stats include fertility treatments and spontaneous conceptions:

1. All fraternal - 95.65%
2. Mixed - 3.83%
3. All identical - 0.52%

I am sure there are sets that I don't have zygosity info for.

MOST Online's survey of 40 quintuplet families (spontaneous and assisted conceptions) found the following zygosity breakdown:

1. All fraternal - 77.5%
2. Mixed identical/fraternal - 15%
3. All identical - none

7.5% were unknown

I had access in my stats to info on all identical sets, while none participated in the MOST study, hence the differences in numbers.

Sextuplets:

The breakdown out of 146 on my list is:

1. All fraternal - 97.26%
2. Mixed - 2.74%
3. All identical - None

MOST Online's survey of 7 sextuplet families found all sets were all fraternal.

Septuplets (updated Aug 04):

1. All fraternal - 97.67%
2. Mixed - 2.33%
3. All identical - None

Only 1 set of septuplets has had identicals in them, which is a rate of 2.33%.

Maternal Age:

Women younger than 20: 1 in 333.33 chance of twins
Women 35+: 10: 1 in 71.4 chance of twins

The most likely age to have twins for white woman is between 35 - 39 (1 in 37) and for black women 35-39 (1 in 32). After 40 the chance diminishes for white women, but continues to be high for black women until age 49.

 © 1997-2009 Jennifer Samson
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