<P> 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 . </P>
<P> 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 . </P>
what percentage of the population has identical twins
what percentage of the population has identical twins
33.3 per 1,000 births
33.3 per 1,000 births