how many sets of twins are there in the us
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 (about 80%) The Yoruba have the highest rate of twinning in the world, at 45 -- 50 twin sets (or 90 -- 100 twins) per 1,000 live births, possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side.