(CBS/AP) When it comes to fertility treatment, women who get three or more embryos implanted have no better odds of conceiving than women who get just two, a new study shows. But those women have a greater chance of risky multiple births.
"Women who have gone through infertility treatment want the best chance of having a baby, but we need to explain that the data shows transferring more embryos doesn't actually do that," said study author Dr. Scott Nelson, head of reproductive and maternal medicine at the University of Glasgow.
In Western Europe, where some countries pay for in-vitro fertilization (IVF), many authorities recommend a single embryo transfer for women under 37 and a maximum of two embryos for women 37 to 40. For women over 40, three is often the limit by law.
Guidelines are relatively lax and unregulated in the U.S., however. The U.S. has seen a rise in multiple births, such as in the case of "octomom" Nadya Suleman. Suleman had octuplets in 2009 after her doctor transferred 12 embryos. She'd already had six children through IVF.
Most fertility treatment in the U.S. is paid for privately and can cost at least $10,000 per cycle, which experts believe encourages the use of more embryos in the belief it will improve odds. During IVF, eggs are fertilized with sperm in a lab dish and then put in the womb.
The American Society for Reproductive Medicine recommends - but does not enforce - single embryo transfers for women under 35. For women 35 to 37, they advise two to three embryos, and three to four embryos for women ages 38 to 40.
For the study, published in the Jan. 12 issue of The Lancet, researchers analyzed data for all 124,000 IVF cycles in the U.K. between 2003 and 2007, which had resulted in more than 33,500 live births. The women were 18 to 50, with varying histories of infertility.
For women under 40 who had two embryos transferred, the live birth rate was 33 percent overall. With three embryos, that dropped to 25 percent, though researchers weren't sure why. Nelson said it might be due to the higher risk of miscarriage in a multiple pregnancy and that miscarrying one fetus would jeopardize the entire pregnancy.
For women over 40, the live birth rate was 13 percent whether they had two or three embryos transferred.
Why do some women get more embryos? Nelson said patients may pressure doctors to transfer more, believing it may boost their chances of having a baby.
"Doctors may feel if they don't do what their patients want, they'll just go down the street to another clinic," he said. "They need legislation to help control the situation."
U.S. data from 2009 showed about 52 percent of embryo transfers involved two while 23 percent used three embryos. Nearly 12 percent involved four to seven or more embryos. Only about 14 percent used one.
Multiple births have a higher risk of problems, including an increased chance of miscarriage complications during pregnancy, including high blood pressure and diabetes. Twins and triplets are more likely to be premature and have an increased risk of developmental problems such as cerebral palsy.
Dr. James Grifo, director of the New York University Fertility Center, agreed doctors should avoid using more than three embryos. But he said it's warranted in some cases, such as older women with a history of failed treatment.
Grifo said the fact many Americans pay for their treatment out of pocket makes a big difference. "I spend a lot of time trying to talk patients out of the three-embryo transfer and you can't always do it," he said.
"My last set of triplets was a patient who demanded I put back three embryos," he said.
Grifo said the patient wasn't swayed by the data. "She delivered the triplets and they're fine, but I wasn't happy about it."