Dec. 1, 2004 -- Couples struggling with infertility often choose in vitro fertilization to achieve pregnancy. Twins are common with in vitro fertilization (IVF). But new research shows that the risk of multiple births can be decreased without lessening the chances of having a baby.
During in vitro fertilization, the egg is fertilized in a lab and implanted into the womb. Traditionally, more embryos are put into the womb during IVF to increase the chances of delivering a baby.
According to a new Swedish study, putting one embryo into the womb during IVF significantly reduces the risks associated with twin births. And the researchers found that this led to similar birth rates as that seen when two embryos were put in simultaneously.
"Couples often don't think of twin births as being that much more risky than a single birth, but it is clear that they are," researcher Christina Bergh, MD, PhD, tells WebMD. "Studies have shown that twins have a five- to 10-times higher risk for whatever poor outcome you measure, including death and malformations."
According to the researchers, the most important factor in determining the number of births is the number of embryos transferred into the womb during IVF procedures.
The researchers tested putting one vs. two embryos into the womb to see if there was a difference in birth rates.
For women that received a single embryo, a second embryo was put into the womb only if the first embryo failed to implant.
This method resulted in a birth rate that was only slightly lower than when two embryos were put in simultaneously -- a 39% birth rate for single-embryo transfer vs. a 43% birth rate for double-embryo transfer.
However, the single-embryo transfer group had significantly fewer multiple births. The twin birth rate among the double-embryo transfer group was 33%, compared with 0.8% for the single-embryo group.
The study is published in the Dec. 2 issue of the New England Journal of Medicine.
Bergh says that single-embryo transfer should be considered for all women undergoing IVF who have a good chance of achieving a pregnancy. Women under 35 with good-quality embryos who have failed no more than one previous IVF attempt are generally considered to be the best candidates.
Patients Are Skeptical
Assisted reproduction specialist Eric Surrey, MD, says it is increasingly clear that for patients with a good prognosis for conception, single-embryo transfer may be preferable to multiple transfers. But he adds that convincing infertile couples of this has been difficult.
"In this country, insurance almost never pays for in vitro fertilization, so maximizing the chances of pregnancy the first time around is a big concern," says Surrey, who is president of the American Society for Reproductive Medicine.
"And couples who don't have children often see twins as a desirable outcome. They look at it as two for the price of one, and when we discuss the risks it seems like a lot of what we say doesn't get heard."
Surrey and colleagues at the Colorado Center for Reproductive Medicine recently published a study on single transfers of five-day-old embryos. The researchers achieved a 61% ongoing pregnancy rate with the single-embryo transfers.
"Even though we offered economic incentives for participating in the study, we still had a hard time recruiting patients for it," Surrey tells WebMD.
U.S. Population Different
The average age of the women who took part in the Swedish study was 30. That is far younger than the typical IVF patient in the United States, and the Swedish women were also less likely to have undergone other assisted reproduction procedures, IVF specialist Owen K. Davis, MD, tells WebMD.
In an editorial accompanying the study, Davis questions the relevance of the Swedish findings for infertile women in the United States.
"It is common practice in the United States to treat young infertile women with 'low-tech' options such as ovulation induction combined with intrauterine inseminations, often for several cycles, before proceeding to in vitro fertilization," he writes.
He adds that women who fail these low-tech treatments may be poor candidates for the single-embryo IVF approach.
Davis tells WebMD that embryo transfer guidelines in the United States were recently changed to urge doctors to consider single-embryo transfers for good-prognosis IVF patients, such as young women.
"Multiple-birth pregnancies are still a significant problem with IVF," he tells WebMD. "The vast majority of twins do just fine, but the risk is considerably higher than for single-birth pregnancies. Having babies one at a time is safest."