Well, in 2009, the twin birth rate was 33.3 per 1000 births.
The birthrate of twins in the US rose 76% from 1980 to 2009
My cousin just gave birth to twin boys Neat, so she has two offspring from the same pregnancy now. Yeah, she had a daughter first but it's still an unexpected surprise. They're fraternal but I don't know what that means. I see, well that means that each of the twins is fertilized by a sperm cell. Oh I see, so it is not from one but two sperm cells. Do you happen to know how common twins are anyway?
The human twin birth rate in the United States, rose 76% from 1980 through 2009, from 18.9 to 33.3 per 1,000 births.