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Single Embryo Transfer

February 24, 2004
American Society for Reproductive Medicine

HIGHLIGHTS FROM ASRM 2004
The 60th Annual Meeting of the American Society for Reproductive Medicine
October 16-20, 2004 - Philadelphia, Pennsylvania

Philadelphia, Pennsylvania - One of the greatest challenges faced by physicians practicing in the field of assisted reproductive technology is to reduce the very high incidence of multiple births resulting from these procedures. As techniques from ovarian stimulation to blastocysts culture to cryopreservation have improved, we are moving closer to the goal of being able to transfer one embryo to a patient per cycle. Single embryo transfer results in fewer multiple pregnancies, by far (although monozygotic twinning is possible) and when performed in the appropriate patient population results in cumulative pregnancy rates as good as those achieved with multiple embryo transfer.

Recent research has found that in many cases, cycles with single embryo transfer are just as likely to result in pregnancy as those in which more embryos are transferred.


Swedish National Policy Requiring Single Embryo Transfer Results in Great Reduction of Multiple Births without Reducing Pregnancy Rates

In a large retrospective study done in a single center in Sweden, researchers evaluated 1664 fresh IVF cycles done between August 2001 and December 2003 to determine the effects of both a regional rule and a decree from the Swedish National Board of Health mandating single embryo transfer. The rule went intoeffect in mid-2002 and the national decree was put in place a half year later- January 1, 2003. Both decrees contain an exception allowing two embryos to be transferred if the risk of twin pregnancy is considered to be low.

The researchers examined data from the three time periods: before any decree, after the regional decree, and after the national decree. Average maternal age and embryo quality scores were similar through the three periods. The percentage of IVF cases utilizing single embryo transfer rose from 25.1% before any decrees were issued to 71.3% after the national decree. While there was no difference in the clinical pregnancy rates for all cycles (single and multiple embryo) for the three time periods. However the twinning rate fell from 22.6% in the first period to 8.8% in the third.(Abstract No.O-320 New Legislation Imposing Single Embryo Transfer. Saldeen and Sundström.)


Rate of Twin Pregnancy Far Lower with Single Blastocyst Transfer; Chances of Pregnancy the Same as for Dual Embryo Transfer

Researchers at the University of Washington also took a look back to see how their center's pregnancy rates for single blastocyst transfer cycles compared to those for two blastocysts.  Looking at blastocyst cycles between January 2003 and August 2004, they found that the 41 single blastocyst transfer cases and 66 cycles in which two blastocysts were transferred resulted in similar implantation and pregnancy rates. Ongoing pregnancy rates for both groups exceeded 75%. Some patients from each group who did not get pregnant after their fresh transfer went on to have transfers of their cryopreserved blastocysts with cumulative pregnancy rates of 83% in both the single and double blastocyst transfer groups. The incidence of twin pregnancy was significantly reduced in the single versus double blastocyst groups (3.2% vs 62%). (Abstract No. O-322 Cumulative Pregnancy Rates Support Elective Single Embryo Transfer. Criniti et al.)


Patients with Embryos to Freeze are
More Likely to Accept Single Blastocyst Transfer

In another study, doctors at Presbyterian Hospital in Dallas, Texas set out to evaluate the patient acceptance rate and the clinical outcomes when single blastocysts transfer was offered to a selected patient population.

Comparing retrospective outcomes between three patient groups (patients who had single blastocyst transfer (SBT), patients who refused SBT, and patients who were identified retrospectively as ones who should have been offered SBT) they found that cumulative pregnancy rates were the same for all groups when fresh and frozen cycles were considered together and that twin pregnancies were reduced from 65% to 2% when a single blastocyst was transferred. Criteria for offering SBT were maternal age of 36 or younger or using donor eggs with two or more quality blastocysts to transfer.

Approximately one third of the patients in this study who were offered SBT accepted it. The SBT group had a second chance to conceive as they always had at least one other quality blastocyst for freezing. Of the patients who elected to have a dual blastocyst transfer, almost half (44%) did not have extra embryos for freezing. (Abstract No. O-89 Towards Single Blastocyst Transfers- Preliminary Experience. Meintjes et al.)

Owen Davis, MD, President of the Society for Assisted Reproductive Technology recommends, "Many patients meet the criteria for single embryo transfer and the practice should become more and more the standard. It is extremely effective in reducing the numbers of multiple births, while maintaining pregnancy rates, and ultimately it might increase patients' chances of having healthy children."

Other Abstracts of Interest:

P-185 Huang et al, Thirty patients underwent single blastocyst transfer, either of their own choosing or because they had only one embryo available. Eighty percent of the elective group became pregnant, while 46% of the non-elective group became pregnant.

P-193 Milki et al, Thirty patients elected to have SBT with cryopreservation of remaining blastocysts. Fifty percent became pregnant in the fresh cycle and others who did not become pregnant in the initial cycle later used their frozen embryos to conceive resulting in a 70% cumulative pregnancy rate.

P-236 Smith et al, A one-year retrospective analysis of all IVF cases progressing to embryo transfer that presented at least one good quality day 5 blastocyst showed selective SET resulting in pregnancy rates similar to those of two-embryo transfers.

The American Society for Reproductive Medicine, founded in 1944, is an organization of close to 9,000 physicians, researchers, nurses, technicians, and other professionals dedicated to advancing knowledge and expertise in reproductive biology. Affiliated societies include the Society for Assisted Reproductive Technology, The Society for Male Reproduction and Urology, the Society for Reproductive Endocrinology and Infertility, and the Society of Reproductive Surgeons.

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