The review included 45 women in their mid-30s or older with good-quality embryos who had single blastocyst transfer. The average age of the women was 37, and the oldest was 43.
Half the women in the review became pregnant after having the procedure - a rate that is roughly double the national average for women in this age group undergoing IVF.
Researcher Amin A. Milki, MD, makes it clear that the women were carefully selected, and that most women of this age group do not have enough good-quality eggs in reserve to allow the transfer of just one embryo.
But for those who have high-quality embryos, single blastocyst transfer offers a good chance at pregnancy with a low chance of giving birth to twins, he tells WebMD.
"We may need to expand the guidelines to include single transfer as an option for good prognosis women over 35 who want to avoid twins for medical or personal reasons," he says.
IVF Over Age 35
The American Society for Reproductive Medicine (ASRM) recommends the transfer of two to three embryos for women between the ages of 35 and 37 and three to four embryos in women between the ages of 38 and 40.
Single-embryo transfer is recommended for women under age 35 who have a good chance of achieving a pregnancy.
Nearly 60% of IVF procedures in the United States are performed on women 35 and older.
Traditionally, single-embryo transfers have been performed only by necessity in women 35 and over because these women had only a single quality embryo available for transfer, Milki says.
He adds that little is known about outcomes in older women with more than one good-quality embryo who chose single blastocyst transfers.
The procedure involves the maturation of embryos outside the body for up to five days, during which time the embryos reach the blastocyst stage of development. The clinician then selects the best-quality embryo for implantation into the uterus.
The 45 women included in the review represented all elective single blastocyst transfers in women over 35 treated at Stanford University Medical
Center in Palo Alto, Calif.
Twenty-eight of the women (62%) conceived and 23 (51%) had pregnancies that went beyond the first trimester and resulted in a live birth.
The review appears in the latest online edition of the journal Fertility and Sterility.
The Trickiest Treatment Group
The findings have the most relevance for women between the ages of 35 and 40 - the age where infertility treatment decisions are often the most complicated, Milki says.
"Younger women can often achieve good pregnancy rates with only one embryo, and the risk of multiple births is low in older women, even when many embryos are transferred," he says.
The challenge in women between the ages of 35 and 40 is to be aggressive enough with treatment to achieve a pregnancy and cautious enough to avoid multiple births.
"Couples understand the medical risks of having triplets, but they are much more accepting of twin pregnancies," Milki says. "When they do understand the risks they are often much more accepting of single-embryo transfer."
Those risks include a sevenfold increase in the chance of premature birth in twin vs. single-child pregnancies, a 1.7-fold increase in long-term handicaps, and a greater chance of giving birth to a child with cerebral palsy, he says.
A recent study found that couples were much less accepting of a pregnancy involving twins when they understood these risks.
Half as many couples considered twins an optimal outcome of infertility treatment after being counseled about the risks.
Reproductive medicine specialist Bradley J. Van Voorhis, D, who led the study team, tells WebMD that the policy at his clinic is now mandatory single blastocyst transfer for patients who have a high risk of delivering twins.
The policy has had little impact on per-patient pregnancy rates, but multiple births have fallen by almost half.
Van Voorhis directs the IVF program, and he is a professor of obstetrics and gynecology at the University of Iowa Carver College of Medicine.
"Patients are pretty accepting of single blastocyst transfer when they realize they still have a good chance of achieving a pregnancy," he says.
By Salynn Boyles
Reviewed by Louise Chang