A new study suggests women undergoing in-vitro fertilization (IVF) should receive no more than two embryos, regardless of their age or the quality of the embryos. But some fertility doctors say the benefits and risks of transferring extra embryos still depend on the woman.

In IVF, a woman's eggs are fertilized outside of her body and the resulting embryos are transferred into her uterus. Because not all embryos will successfully implant and result in pregnancy, doctors often transfer more than one - a practice that increases the odds of multiples and, consequently, the risk of complications.

The British study, which was based on a review of more than 120,000 IVF cycles yielding 33,514 live births in the U.K., found a higher live birth rate and lower complication rate among women who received two embryos compared with women who received three, regardless of their age. Transferring two embryos was associated with a higher live birth rate than transferring one, and the live birth rate was lower among women over 40, irrespective of the number of embryos transferred.

"In older and younger women, the transfer of two embryos was associated with greatest live birth rates," the study authors wrote in their report, published today in The Lancet. "A clear implication of our study is that transfer of three embryos should no longer be supported in women of any age."

The American Society of Reproductive Medicine and the Society for Assisted Reproductive Technology currently recommend transferring no more than two embryos in women younger than 38, no more than four embryos in women aged 38 to 40, and no more than five embryos in women 41 to 42.

Nadya Suleman, better known as "Octomom," gave birth to octuplets in 2009 after Beverly Hills fertility specialist Dr. Michael Kamrava transferred 12 embryos - six times the number recommended for then-33-year-old Suleman. The Medical Board of California revoked Kamrava's license in July 2011.

Dr. Richard Paulson, chief of reproductive endocrinology and infertility at the University of Southern California's Keck School of Medicine, said the decision of how many embryos to transfer depends on the health of the patient and the quality of her embryos. And because the study did not address why women had one, two or three embryos transferred, Paulson said it cannot conclude a link between the number of embryos transferred and the outcome.

"Specifically, a good prognosis patient might be counseled to have fewer embryos transferred," said Paulson. "In contrast, if the embryos do not exhibit favorable characteristics, or the patient has other poor prognostic factors, this patient might be counseled to have three embryos transferred."

The patient might also be compelled to ask for more embryos if she's aware of other fertility problems, Paulson said.

"We are still left with the logical answer that transferring more embryos results in higher probability that at least one embryo will implant. This will lead to a higher pregnancy rate but also a higher risk of multiple implantations which can then lead to multiple gestations and other complications associated with that outcome," said Paulson.

Dr. Sherman Silber, director of the Infertility Center of St. Louis, echoed Paulson's view that doctors are more likely to transfer three embryos if the quality is poor.

"[The American Society of Reproductive Medicine] does object to transferring three embryos in younger women with good quality embryos. However, if a woman is over 40 with poor quality embryos, ASRM of course then does not object to transferring three embryos, and in fact that is not a dangerous practice," said Silber.

The study authors suggested a number of strategies to reduce the risk of multiples from IVF, including public funding to cover treatment costs and improvements in embryo freezing techniques, both of which would allow for more transfer attempts.

"A combination of these factors will increase the likelihood that the outcome of interest will be achieved: one healthy baby at a time," they wrote.