In Dr. van Montfoort's study of unselected patients, significantly more SET patients (52%) had excess embryos available for cryopreservation, compared with the DET patients (40%). However, even after all patients with frozen embryos underwent one subsequent frozen embryo cycle, the ongoing pregnancy rate remained considerably lower (29%) for the SET group, compared with the DET group (42%).
In Dr. Bredkjaer's study of selected patients, 93% of the SET patients had extra embryos cryopreserved, and 35% of these patients became pregnant on a subsequent frozen-embryo transfer.
Despite the promising data, Dr. Jones doesn't expect the European wave of enthusiasm for SET to catch on soon in the United States, and the main reason is financial.
“I don't think it's ever going to happen until it is mandated or there's insurance coverage for fertility treatment in the U.S.,” he said in an interview. “In the Nordic countries there is insurance for IVF, and so patients are willing to undergo several cycles with single-embryo transfer. In the U.S., it's all out of pocket, so they want to get pregnant on the first attempt.”
David K. Gardner, D.Phil., and associates at the Colorado Center for Reproductive Medicine published a study last year showing that with single-blastocyst transfer on day 5 (most European programs do single-embryo transfer on day 3), high ongoing pregnancy rates can be achieved on the first attempt (Fertil. Steril. 2004;81:551–5).
The prospective trial randomized 48 women to either single-blastocyst transfer or double-blastocyst transfer, and investigators found a comparable ongoing pregnancy rate of 61% and 76%, respectively, with a twin rate of zero in the single-blastocyst transfer group and 47% in the double-blastocyst transfer group.
“If SET can be performed with a high degree of success in appropriate patient populations, as is suggested by the current investigation, there are no financial or medical reasons not to recommend this approach,” wrote the Colorado investigators.
Patients were eligible for the study if they met the center's criteria for blastocyst transfer: a day 3 FSH level of 10 mIU/mL or less, an estradiol level of less than 80 pg/mL, a hysteroscopically normal endometrial cavity, and at least 10 follicles measuring at least 12 mm on the day of HCG administration.
The authors acknowledged their difficulty in getting patients to volunteer for SET. “This was undoubtedly due to the perception by patients that SET could result in lower pregnancy rates and that twin pregnancies are a desirable outcome,” they wrote.
Patient attitudes are undoubtedly a barrier to SET, but physicians' attitudes also can have a huge influence, said Christina Bergh, M.D., professor of obstetrics and gynecology at Sahlgrenska University Hospital in Goteborg, Sweden. A study she presented at the meeting found that physicians' attitudes toward SET in the various Nordic countries correlated strongly with the rates of SET and multiple births in those countries. “When aiming for a reduction in multiple births by introducing SET, IVF doctors are important targets,” Dr. Bergh said.
“Most patients rely on doctors for advice,” she said later in an interview. “My experience is they trust us; we are the experts.” Convincing Swedish patients to try SET was much easier than had been expected, she said.
If U.S. physicians face a tougher time convincing their patients to choose SET, some new evidence could boost their powers of persuasion. SET may actually lead to lower miscarriage rates and better neonatal outcomes, compared with singleton pregnancies resulting from the transfer of more than one embryo. It has long been recognized that singletons conceived through IVF have a much poorer outcome than spontaneously conceived singletons.
Now some researchers report that this disparity could possibly be due to the effects of multiple-embryo transfer. Just as a vanishing twin has been shown to increase complications for the surviving fetus, recent evidence suggests that the demise of at least one embryo after a multiple-embryo transfer may create a toxic environment for the implanted surviving embryo.
A study presented at the meeting by Diane De Neubourg, M.D., supports this argument. After prospectively collecting obstetrical and neonatal data on 251 IVF singletons conceived after SET and more than 53,000 singletons that were spontaneously conceived, she found both groups had comparable outcomes.
Although a higher percentage of SET babies than spontaneously conceived babies (9.2% vs. 5.4%) was born prematurely (32–37 weeks), the mean birth weights and mean gestational ages of the groups were similar.
This compares with other studies showing increased perinatal mortality, increased birth rates of small-for-gestational age infants, and increased preterm delivery and low and very low birth weight in IVF singletons (most of whom are conceived after multiple-embryo transfer), said Dr. De Neubourg, a gynecologist at the center for reproductive medicine at Middelheim Hospital in Antwerp, Belgium.