Rate Of Twin Births Soared During Past 30 Years: CDC
January 5, 2012

Rate Of Twin Births Soared During Past 30 Years: CDC

The number of twins born to U.S. women has soared over the past thirty years, primarily due to test-tube babies and women waiting to have children until their 30s, when the chances of having twins increase, according to a report released on Wednesday by the U.S. Centers for Disease Control and Prevention.

The twin birth rate climbed 76 percent from 1980, when 1 of every 53 births was a twin delivery, to 2009, when 1 out of every 30 births were twins.

"When people say it seems like you see more twins nowadays, they're right," said CDC epidemiology Joyce Martin, co-author of the report.

The results were not unexpected, as more women delay starting a family until they are over 30.  For reasons that are not entirely clear, mothers in their 30s are more likely to have twins than younger or older women.

As much as one-third of the increase seen in the study can be attributed to that, with the rest due to fertility drugs and treatments, Martin said.

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

Beginning in the early 1980s, couples that had trouble conceiving began turning to fertility drugs, in vitro fertilization and other fertility techniques.  These treatments became fairly commonplace during 1990s.

The twin birth rate rose, on average, by more than 2 percent per year from 1980 through 2004, when it leveled off to less than 1 percent annually with the exception of 2008 to 2009, when it grew 2 percent.

In 2009, twin rates increased in all 50 states, with the highest increases occurring in lower New England, New Jersey and Hawaii. In Connecticut, twins now account for nearly 5 percent of all births, the CDC study revealed.

Nationally, 3.3 percent of all births were twins in 2009, a 2 percent increase from 1980.

Over the past thirty years, rates of twin births rose for white, black and Hispanic women, although the increases were not uniform.  Rates doubled for whites, rose by half for blacks and by roughly one-third for Hispanics.

Historically speaking, black mothers have twins most often, although white mothers have nearly caught up.

The greatest rise in twin rates was for women 40 years of age and older, who are far more likely to use fertility treatments and to have two embryos implanted during in vitro fertilization.

About 7 percent of total births for women 40 years of age and older were twins, compared with 5 percent of women in their late 30s and 2 percent of women age 24 or younger, the study revealed.

Fertility treatments were not the only factor at play. Indeed, before fertility treatments existed, 2.5 percent of babies born to women in their late 30s were twins, compared with less than 2 percent for younger and older women.  Previous research has suggested that women in their 30s are more likely to produce multiple eggs in a cycle, increasing their chances of twins.

More than one-in-three births have been to women 30 years of age and older, a significant increase from the one-in-five in 1980.

Some experts say the trend of growing twin birth rates is troubling, noting that multiple births are more dangerous for the mother and their infants. Martin says twins are at higher risk because they are more likely be born smaller and earlier, require more hospitalization and to die during their first year of life.


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