Which nation has the highest birthrate of twins in the world?
It's hard for the scientists to define the exact number of twins in the developing world. Anyway, the record for the highest twin birthrate is held by Benin, a small country in West Africa. 28 twins per 1000 births are born here! Such record is amazing with the global average of 13 twins per 1000 birth among all the studied countries.
By the way, the scientific study of twins is known as "gemellology".