The University of Texas estimates 32 out of 1,000 people are a twin, which translates to 3 percent of the population. As of 2009, approximately one in 30 births results in twins.
Race and ethnicity contribute to the incidence of twins. Non-Hispanic black mothers have twins in 3.8 percent of births, and non-Hispanic white mothers have twins in 3.7 percent of births. Hispanic mothers have the lowest incidences, with just 2.2 percent of births resulting in twins. Age also plays a role in twin births. Births in women over the age of 45 result in twins over 20 percent of the time, while mothers in their early 20s give birth to twins just 2 percent of the time.