What is the incidence of twin births?

See below. Monozygotic twin births occur all over the world at a constant rate of 3.5 per 1000 births. Dizygotic twin births range from 6.7/1000 births in japan, to a high of 40/1000 births in nigeria. The two most important factors that influence dizygotic twinning are maternal age at conception, and the use of assisted reproductive technology. Due to the increasing tendency of women to delay pregnancy.
1.4 % The incidence of twins in the US is 1 in 70. This is partially related to fertility treatments and partly due to increased incidence of pregnancy at older ages. Certain ethnic groups, Africans and African Americans have a higher incidence.