About 865,000 more twins have been born in the United States over the last 30 years due to infertility treatments that boosted multiple births.
Statistics released Wednesday by the federal government show that twin births rose 76% from 1980 to 2009. One in every 30 births in 2009 was a twin compared with one in every 53 babies in 1980.
Twin births rose the most among women age 40 and older, who are most likely to undergo in vitro fertilization and other infertility procedures that increase the odds of becoming pregnant with twins. Older age also increases the odds of spontaneous twinning.
But, the researchers noted, the increase in twin births among older women accounts for only part of the surge in twin births. Infertility treatments are common among women age 30 and older. Overall, about two-thirds of the increase in twin births since 1980 is due to infertility treatments.