# Why Are Twins Only Conjoined?
**URL:** https://boards.straightdope.com/t/why-are-twins-only-conjoined/291704
**Category:** Factual Questions
**Created:** [February 24, 2005, 3:04pm UTC](https://boards.straightdope.com/t/why-are-twins-only-conjoined/291704 "2005-02-24T15:04:11Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Jim\_B](https://boards.straightdope.com/u/Jim_B)
#### Post date: [February 24, 2005, 3:04pm UTC](https://boards.straightdope.com/t/why-are-twins-only-conjoined/291704/1 "2005-02-24T15:04:11Z")
…why never triplets, quadruplets, etc.?
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### Author:  [@One\_And\_Only\_Wanderers](https://boards.straightdope.com/u/One_And_Only_Wanderers)
#### Post date: [February 24, 2005, 3:19pm UTC](https://boards.straightdope.com/t/why-are-twins-only-conjoined/291704/2 "2005-02-24T15:19:59Z")
> [@Jim B.](#):
>
> …why never triplets, quadruplets, etc.?
they are according to [this site](http://mypage.direct.ca/c/csamson/multiples/conjoined.html) only 2 cases of all three triplets conjoined, more cases with two out of the three conjoined and one normal
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### Author:  [@Nametag](https://boards.straightdope.com/u/Nametag)
#### Post date: [February 24, 2005, 6:09pm UTC](https://boards.straightdope.com/t/why-are-twins-only-conjoined/291704/3 "2005-02-24T18:09:32Z")
IIRC, conjoined twins are always identical twins, never fraternal. Triplets and higher multiple births are usually fraternal, and rarely identical. Identical twins are produced by a single zygote dividing – conjoined twins by incomplete division. Imagine how unlikely it is to have two or more of these events happen at once.
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [February 24, 2005, 6:48pm UTC](https://boards.straightdope.com/t/why-are-twins-only-conjoined/291704/4 "2005-02-24T18:48:59Z")
Right. It’s very unusual for a zygote to incompletely divide, which is what causes conjoined twins. The odds of it happening twice in a very short time period are very small.