Older Mothers, Fertility Treatments Driving a Big Increase in Twin Births, New CDC Report Says

ATLANTA — The number of twins born in the U.S. soared over the last three decades, mostly the result of test-tube babies and women waiting to have children until their 30s, when the chances of twins increase.

In 2009, 1 in every 30 babies born in the U.S. was a twin, an astounding increase over the 1 in 53 rate in 1980, according to a government report issued Wednesday.

“When people say it seems like you see more twins nowadays, they’re right,” said Joyce Martin, an epidemiologist who co-authored the Centers for Disease Control and Prevention report.

Some increase was expected as more women are delaying starting a family until they are over 30. For some unknown reason, mothers in their 30s are more likely to have twins than younger or older women. As much as a third of the increase can be attributed to that, Martin said.

The rest of the rise is due to fertility drugs and treatments.

“You have a double whammy going on. There are more older moms and more widespread use of fertility-enhancing therapies,” Martin...