ATLANTA  - The number of twins born in the United States has doubled in the last three decades largely as a result of fertility treatments, with one in 30 infants born in 2009 a twin, the Centers for Disease Control and Prevention said on Wednesday.

“The increases are quite widespread, affecting all age groups and all parts of the country,” said Joyce Martin, a CDC epidemiologist and coauthor of the new study. More than 137,000 twins were born in the United States in 2009, accounting for one in every 30 babies.