DAY 6 BLASTOCYST TRANSFERS INCREASE THE PREGNANCY, IMPLANTATION AND LIVE BIRTH RATES COMPARED TO DAY 5 BLASTOCYST TRANSFERS IN HUMAN IVF-ET L.K. Smith, E.H. Roots and M.J. Odom Dorsett The Centre for Reproductive Medicine, Lubbock, TX Introduction Recent advances in ART have made it possible to routinely culture human embryos to the blastocyst stage. Blastocyst culture and transfer has been reported to increase pregnancy and implantation rates and to reduce the risk of higher order multiple pregnancies in human IVF-ET (1-4). Currently, blastocyst transfers are performed primarily on Day 5 of embryo culture. Our laboratory has investigated the possibility that extending the transfer time to Day 6 for all IVF cases might increase pregnancy and implantation rates further, by increasing the efficacy of embryo selection. Objective The objective of this study was to determine if extending embryo transfer time to Day 6 would increase pregnancy and implantation rates. Design A four-year retrospective analysis of all IVF cases with Day 5 or Day 6 embryo transfers from April 15, 1998 to December 31, Materials/Methods Blastocyst culture was performed on all IVF cases. Oocytes were co-incubated with 200,000 motile sperm/mL in 100 µL drops of S1 or G1.2 media (Vitrolife) under mineral oil (Squibb). All cultures were performed in a 37ºC incubator with 5% CO 2. Denuding and fertilization checks were performed at 18 hrs. Embryos were washed and moved to µL drops of S1 or G1.2 media under mineral oil and cultured until Day 3. The embryos were then washed and transferred to µL drops of S2 or G2.2 media under mineral oil and cultured until Day 5 or Day 6. Blastocyst transfers were performed on Day 5 or Day 6 with an 18 cm Wallace transfer catheter. The transfer day was the first day (Day 5 or Day 6) in which the embryologist could select the best 2-3 blastocysts. Only IVF cases with  1 blastocyst by Day 5 were included in the study. All IVF cases that utilized oocyte donors or gestational surrogates were excluded from the study. IVF-ICSI was performed on ~10% of the cases. Statistical analysis of the data was performed using Chi square or Student t-tests where appropriate. Results Table 1: Summary of IVF Cases n % of Cycles Cycles 467 Retrievals % Transfers % ICSI % Cryopreservation % Table 2: Analysis of IVF Cases Day 5 Blastocysts Day 5 Blastocysts Day 5 Transfers Day 6 Transfers Age32.2   4.0 # Prior IVF Cycles 0.7   1.2 # Oocytes Retrieved11.8   4.4 % Fertilization 69.2% 68.5% % Cleavage 84.9% 86.6% % Blastulation 40.7% 43.0% # Blastocysts Transferred 2.4   0.9 Table 3: Day 5 vs Day 6 Blastocyst Transfers Day 5 Blastocysts Day 5 Blastocysts Day 5 Transfers Day 6 Transfers # Transfers Positive ßhCG/Transfer 59.8% (49/82) 77.1% (121/157) * Positive US/Transfer 47.6% (39/82) 63.7% (100/157) * Live Birth/Transfer 43.9% (36/82) 62.4% (98/157) * % Implantation 29.9% (60/201) 48.5% (150/309) * * Results differ from Day 5 transfers at P < 0.01 Chi square. Results are expressed as the percent of blastocysts transferred on Day 6 that would have been selected for transfer on Day 5 or Day 3. * Results differ from Day 6 at p < 0.01 Chi square. Conclusions Day 6 blastocyst transfers increased the pregnancy, implantation and live birth rates compared to Day 5 blastocyst transfers in IVF-ET cases that presented  1 blastocyst on Day 5. These results suggest that blastocyst transfers should be performed on Day 6 for optimal results. The implantation rates of Day 6 blastocyst transfers suggests that acceptable pregnancy rates may be achieved using single embryo transfers. References 1. Gardner DK, Vella P, Lane M, Wagley L, Schlenker T, Schoolcraft WB. Culture and transfer of human blastocysts increases implantation rates and reduces the need for multiple embryo transfers. Fertil Steril 1998;69: Gardner DK, Schoolcraft WB, Wagley L, Schlenker T, Stevens J, Hesla J. A prospective randomized trial of blastocyst culture and transfer in in-vitro fertilization. Hum Reprod 1998;13: Behr B, Pool TB, Milki AA, Moore D, Gebhardt J, Dasig D. Preliminary clinical experience with human blastocyst development in vitro without co-culture. Hum Reprod 1999;14: Marek D, Langley M, Gardner DK, Confer N, Doody KM, Doody KJ. Introduction of blastocyst culture and transfer for all patients in an in vitro fertilization program. Fertil Steril 1999;72: Day 5 BlastocystsDay 6 Blastocysts