More US women having twins; rate at 1 in 30 babies
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 said.
Starting in the early 1980s, couples who had trouble conceiving began to benefit from medical advances like fertility drugs and in vitro fertilization and other procedures. These treatments became fairly widespread in the 1990s but are expensive, and availability and insurance coverage varies.
The twin birth rate rose by more than 2 percent a year, on average, from 1980 through 2004. It leveled off to less than 1 percent annually although the rise from 2008 to 2009 was nearly 2 percent.
In 2009, twin rates increased in all 50 states, though the jumps were highest in lower New England, New Jersey and Hawaii. In Connecticut, twins now account for nearly 5 percent of births.
That’s high. Nationally, 3.3 percent of all births were twins in 2009, up from 2 percent in 1980.
Over the last three decades, rates rose for white, black and Hispanic women, but the increases were not uniform. Rates doubled for whites, rose by half for blacks and by about a third for Hispanics. Historically, black moms have twins most often, but white moms have almost caught up.
“That’s changed with infertility treatments,” said Barbara Luke, a Michigan State University expert on twin births.
The greatest increase in twin rates was for women 40 and older. They are more likely to use fertility treatments and to have two embryos implanted during in vitro fertilization, whereas younger women are more likely to get just one.