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Twin Birth Rate in the U.S. Rose 76 Percent in Two Decades



CDC NCHS released a new data brief this morning on twin births in the United States from 1980 to 2009. Here are the key findings from the report:

• In 2009, 1 in every 30 babies born in the United States was a twin, compared with 1 in every 53 babies in 1980.

• The twin birth rate rose 76 percent from 1980 through 2009, from 18.9 to 33.3 per 1,000 births.

• If the rate of twin births had not changed since 1980, approximately 865,000 fewer twins would have been born in the United States over the last three decades.

• Twinning rates rose by at least 50 percent in the vast majority of states and the District of Columbia.

• Over the three decades, twin birth rates rose by nearly 100 percent among women aged 35–39 and more than 200 percent among women aged 40 and over.

• The older age of women at childbirth in 2009 compared with three decades earlier accounts for only about one-third of the rise in twinning over the 30 years.

Chart appears in the NCHS Data Brief “Three Decades of Twin Births in the United States, 1980–2009”, January 2012. [NCHS Pressroom]





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Reader Comments (4)

I can't get the study to open on the CDC's page. Coul be because I'm on my iPod, but anyway...
Did it give any further breakdown of the numbers? Is the increase found in equal measure for both identical and fraternal twins?
My first inclination is to assume that most of this increase could be attributed to various fertility treatments (IVF, Clomid, etc.) which would seem a likely cause, especially if rates of twinning (identical) stayed the same or rose only slightly since you clearly gave a higher likelihood of conceiving fraternal twins if your ovulation is stimulated and you release multiple eggs, or if you have multiple embryos implanted... But I'm curious to know if the rate of twinning naturally (either type) has gone up as well, which would suggest an environmental cause...

January 5, 2012 | Unregistered CommenterMiriam

Good points, Miriam. I would also guess that only the rate of fraternal twins rose (because of fertility treatments), while identical stayed the same, unless identicals are somehow more likely in older women.

January 5, 2012 | Unregistered CommenterKK

The rate of monozygotic (identical; from one zygote created by the fertilization of one egg by one sperm) twinning is remarkably stable worldwide: it's about 2-3 per 1000. Twinning rates vary dramatically by country, age, etc, because of changes in the frequency of dizygotic (fraternal) twins. But twin zygosity isn't captured on birth certificates. One would assume the increase is all DZ/fraternal twins.

January 5, 2012 | Unregistered CommenterLauren


January 5, 2012 | Unregistered CommenterAshley
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