A new report from the Centers for Disease Control and Prevention found that 1 in every 30 babies born in America in 2009 was a twin, a sharp rise from the 1 in 53 statistic from 1980. Researchers attribute the rise to two main factors--a rise in the number of assisted reproductive technologies, such as artificial insemination and in vitro fertilization, and women waiting until they are over 30 to start their families, both of which are known to statistically increase the likelihood of twin pregnancies.
"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.
Image: Twin babies, via Shutterstock.