It has been well documented that over the past four decades, increases in the use of fertility treatments have coincided with a significant boom in the rate of multiple births in the United States.
Now, a new report has taken a closer look at the trend, finding that in 2011 more than one-third of twin births, and more than three-quarters of all triplet and higher-order births (multiples of three or more) resulted from reproductive treatments.
The study, published in the New England Journal of Medicine on Wednesday, says by 2011, the incidence of triplet or higher-order births decreased by 29 percent from its peak in 1998 -- a trend researchers attributed, in part, to changes in medical guidelines. In 1998, the Society for Reproductive developed for the first time guidelines aimed at reducing multiple births resulting from in vitro fertilization by encouraging limits on the embryos transferred into the woman. Twins and other multiples have a greater risk of being born at a low birth weight, and have been linked to significantly higher health care costs.
"We don't want to overstate it, and say that we've solved the problem," said Dr. Kathy Hoeger, director of the Strong Fertility Center at the University of Rochester, N.Y., who called the findings "positive" -- particularly regarding IVF. "The policy changes at the national level are really helping to guide practice and provide patients with information." Hoeger did not work on the new study.
But as health policymakers have focused their efforts on in vitro, other fertility treatments have overtaken IVF as major sources of multiple births resulting from medical interventions.
"One thing we didn't quite expect is that among the culprits, IVF -- which we always tend to intuitively point fingers at -- remains an actor, but it's not the main offender," the study's senior author, Dr. Eli Adashi, a professor of obstetrics and gynecology at Brown University, told The Huffington Post. "Various non-IVF approaches seem to lead the pack, and account for more and more of the multiples that we see."
Women hoping to conceive are often prescribed ovulation-inducing medications, or undergo insemination, having sperm placed directly into their uterus. And unlike IVF, where doctors can control the number of embryos transferred into the woman, there are fewer ways to control, for example, whether an ovulatory drug such as Clomid will result in multiple births. Often, women are prescribed fertility treatments by doctors who do not necessarily specialize in reproductive endocrinology, meaning patients may be unaware of the risks, Adashi said.
"There are about 50,000 providers of women's health services in the U.S., all of whom are in a position to offer non-IVF technologies," he explained. "In the long run, it takes education, education, education for new insights to diffuse to the entire medical community."
The new report did not find a marked decrease in the rate of twin births: It estimated that the proportion of twin births resulting from medically assisted conceptions rose from 27 percent in 1998 to 36 percent in 2011.
Marilynn Marchione reported for the Associated Press earlier this week, 46 percent of IVF babies are multiples, mostly twins. Groups like the American Society for Reproductive Medicine are attempting to target those rates, updating guidelines so that women under 35 with reasonable odds of success are offered single embryo transfer, and no more than two embryos at one time.
And the need for fertility treatment is high. Estimates suggest that roughly 6 percent of married women between the ages of 15 and 44 in the U.S. are unable to get pregnant after one year of regular, unprotected sex, which is the general definition used for infertility. Around 11 percent of all women age 15 to 44 have difficulty getting pregnant or carrying a pregnancy to term.
"We have a ways to go," said Hoeger, speaking of limiting the risk of multiples. But "in the big picture," she added, "fertility treatments are such a necessary and welcome part of assisting people [who hope to conceive]."
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