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Twin Births Multiply in the United States

In 2009, one in every 30 infants born was a twin. Does that sound like a lot? It is, when you compare it to 1980, when only one in every 53 babies born was a twin.

According to a new CDC report, "Three Decades of Twin Births in the United States, 1980–2009," the twin birth rate rose 76 percent from 1980 through 2009, from 18.9 to 33.3 per 1,000 births. Before that, the incidence of multiple births had remained at about 2 percent of all births from the year 1915 through the 1970s.

Older Mothers, Fertility Treatments, Are Reasons for Growth

While twin birth rates rose among the groups, the largest increase was seen in non-Hispanic white mothers. In addition, while twin birth rates increased for women of all ages, the largest increases were in older women: From 1980 to 2009, rates increased 76 percent for women aged 30–34, nearly 100 percent for women aged 35–39, and more than 200 percent for women aged 40 and over.

While older women are more likely to have twins, women having babies at an older age does not account for all of the large increase, according to the study authors, who wrote:

    " ... older maternal age accounts for only part, or about one-third of the total rise in the twin birth rate over the study period ... Another factor related to the rise in twinning in recent years is the increased use of infertility treatments, both assisted reproductive technologies (ART) (e.g., in vitro fertilization) and non-ART treatments (ovulation stimulation medications without ART). The use of these therapies became more prevalent during the 1980s and 1990s and is more common among women aged 30 and over."

The Risk of Twins

Twins are adorable, but becoming pregnant with twins puts both mother and baby at higher risk. In addition, there is the cost to society due to increased maternal hospitalizations to prevent prematurity, increased intensive care for the babies from prematurity, and increased rates of lifelong disabilities such as cerebral palsy. According to the CDC report:

  • An estimated additional 865,000 twins were born in the United States over the study period due to rising rates.
  • More than one-half of these infants were low birthweight.
  • One in 10 of these infants were very low birthweight.

Single Embryo Transfer for Safe Singleton Pregnancy

With fertility treatments such as IVF, being pregnant with one child is safer with the greatest chance of an healthy pregnancy and birth. Many fertility doctors hope the rates of twin pregnancies will reverse as the days of transferring multiple embryos begin to wane with advances in technology that allow fertility doctors to transfer embryos after five days instead of three, when they have developed to the blastocyst stage.

Research has shown that success rates for single embryo transfer vs. double embryo transfer are similar in certain circumstances.In fact, earlier this year, the Practice Committee of the American Society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technology (SART) recommended an increase in the use of single embryo transfer (SET) in patients undergoing IVF who have a good prognosis.

“The clinical data now make it clear that in good prognosis patients, only one embryo should be transferred,” said Eric Widra, MD, Chair of the SART Practice Committee and a fertility doctor with Shady Grove Fertility Center.


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