Initial experience with extended culture and blastocyst transfer of cryopreserved embryos

OBJECTIVE: Our purpose was to evaluate the viability and transfer efficienc y 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 cryopres erved at either 2 PN (pronuclear) or cleaving stage (day 1-3) were thawed a nd cultured for uterine transfer on day 5. Outcome for day 5 embryo transfe r was prospectively compared with previous outcomes from embryos transferre d on day 2 or 3. RESULTS: For embryos thawed and transferred on day 2 or 3 (n = 99), the pre gnancy 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 pregn ancies having greater than or equal to 3 gestational sacs. For extended cul ture 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 multip le gestations was 33.3% (3/9) with all of these being twins. For embryo tra nsfers performed on day 5 in which only blastocysts were transferred (n = 9 ), the pregnancy rate was 66.7%, the implantation rate per blastocyst was 4 4.4% (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 blast ocyst stage. In this series 4 subjects (15.4%) did not have blastocysts by day 5. CONCLUSION: Acceptable pregnancy rates can be obtained from cryopreserved e mbryos cultured to the blastocyst stage with a significantly higher implant ation rate. Transfer of embryos that have "self-selected" to blastocysts re sults in reduced risk of higher-order (>2) multiple gestations, because onl y 1 or 2 embryos are transferred.