Long-term cryostorage does not adversely affect the outcome of oocyte thawing cycles.

This multi-centre study evaluated systematically the influence of the duration of cryostorage on the outcome of thawing cycles when using slow-frozen oocytes. The thawing cycles were retrospectively divided into three main groups based on cryostorage duration: group A, 1-3 months; group B, 4-6 months; and group C, 7-48 months. Group C was subsequently divided into three subgroups: group C1, 7-9 months; group C2, 10-12 months; and group C3, 13-48 months. Main outcome measures observed were oocyte survival after thawing, fertilization, cleavage; embryo quality and development, implantation, and birth. No significant differences in main outcome measures were observed between all the groups studied. In conclusion, human oocytes can be safely cryostored for several years. This finding could encourage the wider use of oocyte cryopreservation as a clinical procedure in assisted reproduction.

Efficiency of human oocyte slow freezing: results from five assisted reproduction centres.

It has been demonstrated previously that freezing oocytes within 2 h of retrieval increases the efficiency of cryopreservation via a slow-freezing/rapid-thawing protocol with 0.3 mol/l sucrose (SF/RT 0.3). The aim of this multicentre survey was to verify this observation on a larger scale. This was a retrospective study on the clinical outcome of 510 SF/RT 0.3 cycles divided into two groups: group A, freezing oocytes within 2 h of retrieval; group B, freezing oocytes more than 2 h after retrieval. The rate of best-quality embryos was significantly higher (33.24%) in group A than in group B (16.20%, P < 0.001). Pregnancy and implantation rates were 30.07% and 15.08% in group A versus 8.97% and 4.57% in group B (P < 0.001). Clinical pregnancy rates per thawed and per injected oocyte in group A were 5.53% and 10.41%, versus 1.46% and 2.77% in group B (P < 0.001). The overall yield from oocytes cryopreserved within 2 h of retrieval (group A) was 6.49 implantations per 100 oocytes thawed versus 1.74 for group B (P < 0.001). Embryo quality, pregnancy and implantation rates, and clinical efficiency of thawing cycles were all significantly improved when cryopreservation was carried out within 2 h of oocyte retrieval.

Construction of an evidence-based integrated morphology cleavage embryo score for implantation potential of embryos scored and transferred on day 2 after oocyte retrieval.

BACKGROUND: Evidence-based morphological embryo scoring models for ranking of implantation potential are still scarce, and the need for a precise model increases when aiming for singleton pregnancies. METHODS: Prospectively, 2266 IVF/ICSI double-embryo, day 2 transfers were studied. The five variables scored in 3- to 5-step scales for the embryos transferred are blastomere number (BL), fragmentation, blastomere size variation ('equality', EQ), symmetry of the cleavage and mononuclearity in the blastomeres (NU). The scoring results of embryos with an individual traceability from scoring to implantation, i.e. treatments resulting in either no implantation (n=1385) or twin implantation (n=228), were studied for prognostic potential. RESULTS: Although all five variables correlated highly with implantation potential, only BL, NU and EQ remained independently significant after regression analysis. The equation thus derived formed the basis for a 10-point integrated morphology cleavage (IMC) embryo score. A table with the scoring point for each possible combination of the embryo variables is presented. The scoring model was statistically validated on the singleton pregnancy group (n=653). CONCLUSIONS: We suggest that this IMC embryo scoring, incorporating cleavage stage and information on the variation in blastomere size and the number of mononucleated blastomeres, may optimize embryo ranking and selection for day 2 transfers.

Pronuclear orientation, polar body placement, and embryo quality after intracytoplasmic sperm injection and in-vitro fertilization: further evidence for polarity in human oocytes?

Three hypotheses were tested: (i) the distance between first and second polar bodies (PB) may relate to embryo morphology, (ii) that the orientation of pronuclei (PN) relative to PB may relate to embryo morphology, (iii) that the placement of a spermatozoon in a fixed plane relative to the first PB [intracytoplasmic sperm injection (ICSI)] may alter PN/PB orientation relative to in-vitro fertilization (IVF). A total of 251 two pronuclear (2PN) embryos (124 ICSI, 127 IVF) from 64 patients was studied. Angles were measured between the PN axis and the nearest PB (alpha), the furthest PB (beta), and between the two PB (gamma). On day 2, the morphological grades of embryos were recorded. gamma ranged from 0 to 150 degrees and was not significantly different for ICSI or IVF embryos of different grades; however, an unusual distribution of gamma suggested different populations of oocytes. The first hypothesis was rejected. alpha and beta ranged from 0 to 90 degrees : alpha did not relate significantly to embryo grade, but beta increased significantly with decreasing quality of ICSI embryos (P < 0.05) and the total group (P < 0.01), supporting hypothesis (ii). The difference in beta between ICSI and IVF embryos was not significant, so hypothesis (iii) was unproven. Significant differences between ICSI and IVF embryos in PN positions, irregular cleavage, and cleavage failure were noted.