More than 3% of U.S. births in 2009 were twins
The number of U.S. twin births per year more than doubled from 1980 to 2009, according to newly released National Center for Health Statistics data.
The report, which did not include babies born in triplets or other multiple pregnancies, found that one in 30 babies born in the United States in 2009 was a twin, up from one in 53 babies born in 1980. As a result, the overall number of twins born nationwide rose from 68,000 in 1980 to more than 137,000 in 2009.
Epidemiologist and study coauthor Joyce Martin attributes as much as one-third of the increase to women waiting longer to have children. According to the report, the rate of twin births among women ages 35 to 39 increased by 100%, and the rate among women ages 40 and older increased by more than 200%. Martin attributed the rest of the increase to fertility drugs and treatments.
According to Martin, twin births generally are riskier than single births. For example, more than half of the additional 865,000 twins born from 1980 to 2009 had low birth weights (Stein, "Shots," NPR, 1/4; Wetzstein, Washington Times, 1/4; Stobbe, AP/Google News, 1/4; Beasley, Reuters, 1/4).