PHILADELPHIA — Results of two new U.S. studies may help dispel fears that single blastocyst transfer results in poor pregnancy success rates. The studies were presented at the annual meeting of the American Society for Reproductive Medicine.
Single blastocyst transfer, which is widely practiced in Europe, guarantees a reduction in multiple births, the biggest problem facing fertility specialists worldwide.
Although triplet pregnancies have been reduced dramatically in the United States by limiting the number of embryos transferred, twin pregnancies still make up roughly one-third of all births from assisted reproductive technology (ART). The most recent figures from the Centers for Disease Control and Prevention show that in 2001 64% of ART births were singletons, 32% were twins, and almost 4% were triplets or other higher order multiples. More than three embryos were transferred in roughly 66% of the ART cycles.
Despite recently released guidelines from the American Society for Reproductive Medicine (ASRM), which suggest consideration of single embryo transfer in patients with the most favorable prognosis (Fertil. Steril. 2004;82:773-4), there has been considerable resistance to this practice in the United States. Many physicians and patients fear that single embryo transfer may reduce overall pregnancy rates. The failure of an in vitro fertilization (IVF) cycle is a financial burden that rests almost entirely on U.S. patients' shoulders. In contrast, the cost of IVF is covered by the national health care systems of most European countries.
Results of the two studies presented at the meeting may help change some people's opinion about the practice. “We feel strongly that single blastocyst transfer is the way to go,” said Marius Meintjes, Ph.D., scientific director of assisted reproductive technology services at Presbyterian Hospital of Dallas.
He presented a 3-year retrospective study that examined live birth rates and twinning rates among 103 patients who had single blastocyst transfer (SBT) and 290 who had double blastocyst transfer (DBT). To be eligible for SBT, patients had to be 37 years of age or younger or be receiving donated oocytes. Patients had to have at least two excellent quality embryos to choose from on the day of transfer. The excess embryos were frozen, and if the patient failed to become pregnant during the fresh cycle, the clinic agreed to pay for subsequent frozen embryo cycles free of charge.
The SBT group had a slightly higher rate of live births/ongoing pregnancies in the fresh cycle, compared with the DBT group (79% vs. 70·9%). But the cumulative rate, which included both fresh and frozen cycles, was not significantly different between groups (79·6% vs. 83·4%). In contrast, the rate of twins was significantly less in the SBT group (2% vs. 68%). There was one case of monozygotic twinning in the SBT group. These results are an important contribution toward convincing patients and physicians that SBT won't decrease the chance of pregnancy, but will reduce the risk of twins. “Patient education is also critical, because there is too much of a perception that twins are OK. This is probably our biggest challenge,” said Dr. Meintjes, adding that the clinic's offer to cover the extra costs of undergoing a frozen cycle removed a financial barrier to SBT.
Roughly one-third of patients who were offered SBT accepted, and almost half of the DBT group had no option for SBT because they didn't have a second good quality blastocyst for freezing.
Another retrospective study had similar findings. Amy R. Criniti, M.D., of the University of Washington, Seattle, and her colleagues compared good prognosis IVF cycles in which one blastocyst (44 cycles) or two blastocysts (66 cycles) were transferred.
Although pregnancy rates in the fresh cycle were slightly higher in the DBT group (79% vs. 76%), when the results from frozen cycles were included, the cumulative pregnancy rate was 83% in both groups. Once again, the SBT group had a significantly smaller percentage of twin pregnancies (3% vs. 62%). There was one case of monozygotic twinning in the SBT.
Eligibility for SBT included age less than 38 years, no previous failure of an IVF cycle, no endometriosis, a normal endometrium at the time of HCG administration, a normal uterine cavity, and at least three blastocysts available on the day of transfer, Dr. Criniti said.
In the United States there has been considerable resistance to transferring only one embryo during an IVF cycle. Courtesy Marisu Meintjes, Ph.D.