Growing numbers of parents are seeing double these days. A new analysis of birth records has found one in every 30 babies born in the United States is a twin.
For comparison, in 1980 just one in every 53 births produced twins.
The reason for the rise: The increased availability of fertility treatments, which boost the likelihood of multiple births, particularly for women having children at older ages.
The findings -- based on 2009 data (the most complete recent figures available) -- were presented by Michigan State University researchers this week at the 14th Congress of the International Society of Twin Studies in Florence, Italy.
The study’s lead researcher Barbara Luke said the trend has important health implications, citing greater risks of death and illness, as well as higher health care costs, associated with multiple births.
"Prior to 1980, the incidence of U.S. twin births was stable at about 2 percent of all births, but it has risen dramatically in the past three decades," said Luke, noting twin births increased for women of all ages, with the greatest rate among women aged 30 and older. "Older maternal age accounts for about one-third of the rise, and two-thirds is due to the increased use of fertility treatments."
About 12 percent of U.S. women have had fertility therapies, including assisted reproductive technologies and ovulation stimulation medications.
Luke, who first reported the numbers in a report with Centers for Disease Control and Prevention researchers, noted births for triplets and higher numbers also grew: one in every 651 babies in 2009, compared with one in 2,702 in 1980.