For our Choice Mom Guide: About Embryos, I asked Choice Mom sponsor Dr. Rafat Abbasi, of Columbia Fertility Center (D.C.) to talk about the difference between transferring an embryo on Day 3 of growth compared to Day 5.
“Over the last several years, the development of culture systems has improved the ability of embryos to reach the blastocyst stage in vitro. It is at this stage [five days after fertilization] that embryos normally implant in the uterus.
Research has shown that the nutritional requirements of embryos change when they reach 8 cells. Newer sequential culture media has become available that support the continued growth in the laboratory. A blastocyst has an inner cell mass (which gives rise to the fetus) and an outer layer of cells surrounding this cell mass. This is the trophectoderm and develops into the placenta.
Several papers have been published (Glujovsky et al)* that report the benefits of day 5 transfers. A high percentage of cleavage stage embryos (day 3), undergo arrest during culture due to the high incidence of aneuploidy (abnormal chromosome number). A study published by Racowsky et al* in 2000, reported that if there were no 8-cell stage embryos (i.e., development was slow), then a transfer on that same day may be considered. But if there were more than three 8-cell stage embryos available, a day 5 blastocyst transfer would be preferred.
Patient selection in deciding which day to transfer the embryos is very important. For good prognosis patients (young age, good ovarian response, no previous failed attempts, high quality of embryos and of reasonable number), an increased live birth rate has been reported together with a lower multiple pregnancy rate with a day 5 transfer.
What are the advantages of a Day 5 transfer?
- Selection of the most viable embryo.
- Potential to use eSET to minimize multiple pregnancy rates.
- Synchronization of the lining and the embryo.
- The potential for preimplantation genetic screening by biopsy.
- Fewer and healthier number of embryos will be cryopreserved.
- Increase in implantation rates… and live birth rate.
The greatest risk is that of a canceled transfer with extended culture in an unselected population of patients, but there is no difference in good prognosis candidates. (Papanikolaou et al).*
In our practice, blastocyst culture has increased over the last 3 years. The excellent survival rates after thawing frozen blastocysts as well as the ability to test the embryos has increased the implantation rates. Most of our patients will undergo blastocyst transfers to also minimize the risk associated with multiple pregnancy. The challenging question is to determine which day 3 embryo will progress to day 5. Several clinical trials including time-lapse studies are underway to try to answer this.
1) Glujovsky D, Blake D, Farquhar C, Bardach A Cochrane Database Syst Rev 2012.
2) Racowsky C, Jackson K, Cekleniak N, Fox J, Hornstein M, Ginsburg E. Fertil Steril 2000.
3) Pamanikolaou EG, Kolibianakis EM, Tournaye H, Venetis CA, Fatemi H, Tarlatzis B. Hum Reprod 2008.