I don't actually know, though the twin rate rose 76% between 1980 and 2009, ending up at 33.3 for every 1,000 births.
Well, the twin birth rate in the US rose from 18.9 to 33.3 for every 1,000 births between 1980 and 2009
I have a twin in real life and when people see us together, I get real sick of them asking if we are twins! How interesting! A developing fetus is called a singleton if they are alone but a multiple if there is more than one developing! Those embryos sure like multiplying! I wonder if twins are more rarer than triplets?
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.