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IVF technique enables pregnancy without multiple births, Stanford researchers find

October 02, 2007

STANFORD, Calif. - An in vitro fertilization technique that can avoid multiple births appears to be effective for women older than 35, according to researchers at the Stanford University School of Medicine.

More than half the women in a retrospective study became pregnant after undergoing the procedure, called a single blastocyst transfer, which transferred just one embryo into the womb.

Nearly 60 percent of IVF procedures in the United States are performed on women older than 35, and the study's senior author, Amin Milki, MD, believes the findings are good news for those women who wish to become pregnant with just one child.

"Although these results represent a selected group of patients, we believe that they should serve as encouragement to patients and providers who are considering single blastocyst transfer in the older IVF population," Milki and his co-authors noted in the study, which was recently published online in the journal Fertility and Sterility.

During the transfer procedure, an embryo is bathed in a culture of nutrients for five days until it reaches a developmental landmark known as the blastocyst stage. At that point, doctors are able to determine which embryos are most likely to thrive long term; they then transfer the best-quality ones into a woman's uterus.

The American Society for Reproductive Medicine currently recommends that doctors transfer two or more embryos into women older than 35, in an effort to maximize a patient's chance of becoming pregnant. This practice can lead to twins or higher-order multiples - as well as subsequent health risks - but Milki said this doesn't stop most patients from undergoing the procedure.

"Many patients would prefer not to have two babies at once," said Milki, professor of obstetrics and gynecology and director of Stanford's IVF program. "But because the success rate is higher when multiple embryos are transferred, women are willing to take the gamble."

In recent years, many reproductive specialists - especially those in Europe - have embraced single embryo transfer as a way to prevent multiple gestations. And data now exist showing the procedure's effectiveness among women of younger reproductive age.

Scant data exist on single blastocyst transfer in women over 35, so Milki and his colleagues decided to review the outcomes of older patients who underwent the procedure at Stanford. Milki said the procedure had been offered to those women with good-quality embryos, and the patients who elected to have only one embryo transferred did so as a way to avoid twin pregnancy. He noted that half the patients already had one child and wanted just one more, while others hoped to avoid the health complications associated with carrying multiples.

After reviewing the data from 45 patients ranging in age from 35 to 43 (with a mean age of 37.3), Milki and his colleagues found that 28 patients (62.2 percent) conceived, and 23 (51.1 percent) had pregnancies that went beyond the first trimester. Milki called this an "excellent pregnancy rate" - especially considering that the national success rate of IVF procedures for women in this age group is around 25 percent. But he pointed out that the women in this study all had good-quality embryos and had a relatively good chance of becoming pregnant.

"This offers reassurance that a woman can still expect a good pregnancy rate without gambling with twins," said Milki. He added that the findings demonstrate a "clear role" for the procedure in older IVF patients, and he said Stanford's IVF program plans to continue offering the procedure as an option for patients.

Milki did caution that the findings are not applicable to every woman over the age of 35. For women with lower-quality embryos, transferring two or three embryos might be the better way to pursue a pregnancy.

Stanford University Medical Center