Initial experience with extended culture and blastocyst transfer of cryopreserved embryos

OBJECTIVE: Our purpose was to evaluate the viability and transfer efficiency of cryopreserved embryos allowed to develop into blastocysts in extended culture for in vitro fertilization. STUDY DESIGN: The embryos for in vitro fertilization that had been cryopreserved at either 2 PN (pronuclear) or cleaving stage (day 1-3) were thawed and cultured for uterine transfer on day 5. Outcome for day 5 embryo transfer was prospectively compared with previous outcomes from embryos transferred on day 2 or 3. RESULTS: For embryos thawed and transferred on day 2 or 3 (n = 99), the pregnancy rate was 33%, the implantation rate per embryo transferred was 15.2%, and the rate of multiple gestations was 42.4% (14/33) with 35.7% of pregnancies having greater than or equal to 3 gestational sacs. For extended culture embryos transferred on day 5 (n = 25), the pregnancy rate was 36%, the implantation rate per embryo transferred was 16.7%, and the rate of multiple gestations was 33.3% (3/9) with all of these being twins. For embryo transfers performed on day 5 in which only blastocysts were transferred (n = 9), the pregnancy rate was 66.7%, the implantation rate per blastocyst was 44.4% (greater than the rate for the day 2 or 3 embryos, P = .0043), and the rate of multiple gestations was 33.3% (2/6) with all of these being twins. In extended culture 29.8% of cryopreserved embryos progressed to the blastocyst stage. In this series 4 subjects (15.4%) did not have blastocysts by day 5. CONCLUSION: Acceptable pregnancy rates can be obtained from cryopreserved embryos cultured to the blastocyst stage with a significantly higher implantation rate. Transfer of embryos that have "self-selected" to blastocysts results in reduced risk of higher-order (>2) multiple gestations, because only 1 or 2 embryos are transferred.