Researchers analyzed close to 125,000 in vitro fertilization (IVF) cycles performed in the U.K. over a five-year period in one of the largest studies ever to compare outcomes in women younger than 40 to those of older women.
The conclusion that there is no medical justification for transferring three or more embryos, even in women over the age of 40, has major implications in the U.S., where 1 in 3 IVF procedures involves the transfer of more than two embryos.
While that represents a decline from a decade ago, when closer to 2 out of 3 IVF procedures in the U.S. involved three or more embryos, there is still plenty of room for improvement, a study co-author says.
"The practice of transferring multiple embryos is very much market-driven in the United States," says Scott M. Nelson, MD, PhD, of the University of Glasgow Centre for Population and Health Sciences. "There is an economic incentive for transferring more embryos in the U.S., but no sound medical reason for doing so."
New York infertility specialist Glenn L. Schattman, MD, disagrees. Schattman is president of the Society for Assisted Reproductive Technology (SART).
SART guidelines call for the transfer of one or two embryos per IVF cycle in younger patients with the best prognosis, and as many as four embryos per cycle in patients in their late 30s and 40s with a poor chance of achieving a pregnancy.
He says it is clear from SART's own statistics that the poorest-prognosis patients have a much better chance of having a baby when more than two embryos are transferred.
"There is a continuous and constant decline in fertility with increasing age, so it makes no sense to treat a 39- or 40-year-old the same way we would a 26-year-old," he says.
The 124,148 IVF cycles analyzed by Nelson and colleague Debbie A. Lawlor, PhD, of the University of Bristol, resulted in 33,514 live births.
The live birth rate was greater with the transfer of two embryos, compared to one, in women under the age of 40 and in women who were older. Transferring three embryos resulted in a lower birth rate than transferring two in the younger women and made no difference in outcomes in older women.
Compared to single-embryo transfer, transferring two or three embryos was associated with a higher risk for all adverse birth outcomes, including low birth weight and preterm delivery.
Not surprisingly, the overall live birth rate was lower in older women compared to younger ones, no matter how many embryos were transferred.
"A clear implication of our study is that [the] transfer of three embryos should no longer be supported in women of any age," Nelson and Lawlor write.
Infertility specialist Liv Bente Romundstad, MD, PhD, of Norway's St. Olavs University Hospital and the Norwegian University of Science and Technology, says the large number of multiple births in the U.S. resulting from IVF procedures illustrates the problem with multiple embryo transfers.
According to a 2009 CDC report:
"It is still common in the United States for doctors to transfer three or more embryos," Romundstad says. "This study shows that three embryos does not result in more live births and it does result in more complications."