Alexis C. Madrigal writes in The Atlantic There Really Are So Many More Twins Now
"From about 1915, when the statistical record begins, until 1980, about one in every 50 babies born was a twin, a rate of 2 percent. Then, the rate began to increase: by 1995, it was 2.5 percent. The rate surpassed 3 percent in 2001 and hit 3.3 percent in 2010. Now, one out of every 30 babies born is a twin."
"Older women tend to have more twins than younger women—and older women are having more of the nation's babies. The researchers found this demographic phenomenon accounted for one-third of the increase. They attributed the rest of it to the increase in infertility treatments, specifically in-vitro fertilization and "ovulation stimulation medications." "
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