Cleavage rate was 98% (67/68) in the in-vivo group and 89% (35/39) in therescued IVM group (NS). 48 out of 68 embryos (71%) developed to blasto-cyst by day-6 in the in-vivo group, and 6 out of 39 embryos (15%) were ob-served in the rescued IVM group (P<.0001). Embryo transfer was performedonly from the in-vivo matured group. 11 embryo transfers were performedwith average 2.5 embryos per transfer, and 10 pregnancies were achieved(91%). A total of 15 FCA were detected in 8 recipients (implantation:15/21, 71%).

CONCLUSIONS: The present study demonstrates that both in-vivo andrescued IVM oocytes provide high survival rate after thawing; but fertiliza-tion rate and embryo development potential from in-vivo matured group weresignificantly higher than the rescued IVM group. However, the rescued IVMoocytes may serve as an adjunct to extend the pool of total cryopreservedoocytes.

Supported by: Organon Pharmaceuticals USA, Inc.; Grant #: 142-05-51.

P-721

DAY 6 BLASTOCYST CRYOPRESERVATION: IT’S WORTH THEWAIT. D. Dasig, M. Dangcil, T. Telles, L. Eways, J. Proctor, W.-H. Shen.OB/GYN, Kaiser Permanente Center for Reproductive Health, Fremont, CA.

OBJECTIVE: To compare survival, implantation and clinical pregnancyrates where blastocysts were frozen on day 5 (D5) or day 6 (D6) of cultureand subsequently thawed and assisted hatched in a frozen embryo transfer(FET) cycle.

DESIGN: Retrospective analysis of autologous blastocyst FET cycles.MATERIALS AND METHODS: FET blastocyst cycles between May

2005 and March 2007 were reviewed. Embryos were cultured in a reducedoxygen environment (5%) sequentially using Quinn’s Advantage Cleavageand Blastocyst Medium each supplemented with 10% v/v Serum ProteinSupplement. Patients either had a D3 or D5 embryo transfer. Good qualityblastocysts developing on D5 or D6, of grade 3BB or better were cryopre-served and thawed using Menezo’s 2-step slow freezing/thawing protocols.Blastocysts were thawed on the morning of the 7th day of progesterone sup-plementation. Those frozen on D5 were preferentially thawed first vs. thosefrozen on D6 if blastocysts from both days were available, until the desirednumber of surviving blastocysts to transfer was achieved. Assisted hatchingwas performed using an infrared 1480 nm diode laser. Embryos were cul-tured 2 hours prior to transfer. Blastocyst showing at least 50% intact cellswere considered viable and selected for transfer. Clinical pregnancy was con-firmed by a clear gestational sac and fetal heart at 6 weeks of gestation. Datawere analyzed using Chi Square analysis.

RESULTS: A total of 40 FET cycles were analyzed. 23 cycles had only D5blastocysts thawed and 17 cycles had only D6 blastocysts thawed. 55 of 57blastocysts frozen on D5 survived (96%) following thawing. Clinical preg-nancies resulted in 74% (17/23) of cycles using blastocyst frozen on D5with an implantation rate of 51% (28/55). For blastocysts frozen on D6, 25blastocyst were thawed with 24 surviving (96%). A clinical pregnancy wasachieved in 11 out of 17 (65%) of these cycles with an implantation rate of60% (15/25). Blastocyst survival, implantation and clinical pregnancy ratesdid not show significant differences between the two groups (P%1) foreach analysis.

CONCLUSIONS: With an optimized culture environment, these data sug-gest that blastocysts frozen on D5 and D6 yield similar survival, implantationand clinical pregnancy rates when used in a frozen embryo transfer cycle. D6blastocysts although delayed in development still have a high potential to im-plant and result in clinical pregnancies and therefore should be considered forcryopreservation and use in frozen embryo transfer cycles.

Supported by: None.

P-722

SHOULD EMBRYOS DESTINED FOR CRYOPRESERVATION BEGROWN TO BLASTOCYST? S. L. Dovey, B. A. Malizia, J. Witmyer,A. S. Penzias. Obstetrics and Gynecology, Beth Israel Deaconess MedicalCenter, Boston, MA; Boston IVF, Waltham, MA.

OBJECTIVE: The favorable pregnancy rates associated with blast transferwere previously outweighed by the difficulty in maintaining embryo devel-opment to the blastocyst stage. With the introduction of sequential media,cryopreservation at the blastocyst stage is now more feasible. Our goal isto examine whether there is a difference in the average number of embryosfrozen per cycle on day 3 vs. those grown to blast, as well as to assess thedifference in thaw survival and clinical pregnancy rates between day 3 em-bryos vs. blastocysts.

FERTILITY & STERILITY�

DESIGN: Retrospective analysis.MATERIALS AND METHODS: All IVF cycles at the Boston IVF center

resulting in at least one cryopreserved embryo from Jan 2000 through Jan2007 were examined to determine the average number of embryos cryopre-served per cycle in the day 3 embryo group and the blastocyst group. Everythaw cycle performed within the same time frame was assessed to determinethe average number of embryos thawed, the average number of embryos tosurvive thaw, and the average percent survival between the day 3 groupand the blastocyst group.

RESULTS: An average of 3.70 embryos were frozen per cycle in the groupundergoing cyropreservation on day 3 vs. 2.67 embryos per cycle among theblastocyst group (P<.05). Average thaw survival among day 3 embryos was74% compared to 85% among the blastocysts (P¼0.05). The clinical preg-nancy rate per thaw cycle among the day 3 embryos and the blastocystswas 34.3% and 40.6%, respectively (P¼0.36).

TABLE 1. Cryopreservation of Embryos Day 3 vs. Blast

Aveage

Total #cycles

Ave #eggs

Ave #mature

Ave #fertilized

Ave #embryotransfer

Ave #frozen

Day 3

34.3 3332 13.91 11.69 9.29 2.33 3.70 Blast 33.9 250 16.56 14.30 11.72 1.96 2.67

TABLE 2. Thaw Cycle Outcomes Day 3 vs. Blast

Aveage

Total #cycles

Ave #thaw

Ave #survived

Ave #embryotransfer

Ave %survival

Clinicalpregnancy

rate

Day 3

36.4 2626 3.47 2.44 2.19 74% 34.3% Blast 35.6 187 2.96 2.21 1.77 85% 40.6%

CONCLUSIONS: Although one additional embryo will be gained by per-forming cryopreservation on day 3 vs. at blast, this appears to be clinicallyinsignificant given that blastocysts are superior in surviving the thaw processas well as in establishing clinical pregnancies. The long time period overwhich this data has been accrued underestimates, if anything, the true supe-riority of blastocyst freezing given recent technological improvements infreeze/thaw processes. Routinely growing embryos destined for cryopreser-vation to blast may result in improved pregnancy rates among patients under-going thaw cycles.

Supported by: None.

P-723

S3 VITRIFICATION: A SAFE, SIMPLE, AND SUCCESSFULMETHOD FOR BLASTOCYST VITRIFICATION. J. J. Stachecki,S. M. Willadsen, K. Wiemer, J. Garrisi, J. Cohen. Tyho-Galileo ResearchLaboratories, Livingston, NJ; Northwest Center for Reproductive Sciences,Kirkland, WA; The Institute for Reproductive Medicine and Science, Living-ston, NJ.

OBJECTIVE: Vitrification is becoming an established way of storing em-bryos, but a safe, easy, and effective procedure has eluded researchers due toshortcomings of current techniques. We examined the effectiveness of a dif-ferent vitrification method for human blastocysts.

DESIGN: Current vitrification protocols, although successful, have short-comings making them difficult to use effectively. Problems include use of di-methylsulfoxide, a relatively toxic cryoprotectant; micro-sized containersthat are often open to contamination and difficult to manipulate; and short ex-posure times that are technically difficult leaving no room for error. We de-vised a different technique (S3 vitrification) that avoids these problems byusing a large, sterile, sealable container, and longer exposure and handlingtimes.

MATERIALS AND METHODS: Blastocysts from IVF patients that con-sented for freezing or research were vitrified. Also, bovine blastocysts werevitrified. Blastocysts were incubated in 2 solutions with ethylene glycol at23�C for 5 min each, transferred to a vitrification solution of glycerol and eth-ylene glycol for 2 min while loading into a sterile 0.25 cc straw, heat-sealed,and vitrified. Straws were thawed for 5 sec in air then 10 sec in 30�C water.

S347