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BACKGROUND: Pronuclear morphology has been proposed as an indicator of embryo development and chromosomal complement. In this study, the morphology of pronuclear zygotes generated from euploid oocytes [diagnosed by first polar body (PB1) analysis] was evaluated and compared with the configurations observed in chromosomally normal embryos (diagnosed by blastomere analysis). MATERIALS AND METHODS: Group 1-238 patients underwent 273 assisted conception cycles in combination with the screening of aneuploidy on PB1 for the chromosomes 13, 15, 16, 18, 21 and 22. Only normal oocytes were inseminated. Group 2-218 patients underwent 318 assisted conception cycles with aneuploidy screening on day 3 embryos. In both groups, oocytes were checked for fertilization and pronuclear morphology at 16 h after insemination. RESULTS: Seventy-three percent of zygotes from Group 1 had the configurations with centralized and juxtaposed pronuclei, large-size aligned or scattered nucleoli and PB located in the longitudinal or perpendicular axis of pronuclei. In Group 2, these configurations corresponded to those with the highest proportion of chromosomally normal embryos. Accordingly, in both groups, these configurations had a higher implantation rate than all the others. CONCLUSIONS: These observations confirm that some patterns of pronuclear morphology are associated with a higher proportion of euploidy and implantation reaffirming the relevance of this scoring system for the prediction of zygote viability.

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BackgroundHuman mature oocytes are very susceptible to cryodamage. Several reports demonstrated that vitrification might preserve oocyte better than slow freezing. However, this is still controversial. Thus, larger clinical, biological and experimental trials to confirm this concept are necessary. The aim of the study was to evaluate and compare fine morphological features in human mature oocytes cryopreserved with either slow freezing or vitrification.MethodsWe used 47 supernumerary human mature (metaphase II) oocytes donated by consenting patients, aged 27-32 years, enrolled in an IVF program. Thirtyfive oocytes were cryopreserved using slow freezing with 1.5 M propanediol +0.2 M sucrose concentration (20 oocytes) or a closed vitrification system (CryoTip Irvine Scientific CA) (15 oocytes). Twelve fresh oocytes were used as controls. All samples were prepared for light and transmission electron microscopy evaluation.ResultsControl, slow frozen/thawed and vitrified/warmed oocytes (CO, SFO and VO, respectively) were rounded, 90–100 μm in diameter, with normal ooplasm showing uniform distribution of organelles. Mitochondria-smooth endoplasmic reticulum (M-SER) aggregates and small mitochondria-vesicle (MV) complexes were the most numerous structures found in all CO, SFO and VO cultured for 3–4 hours. M-SER aggregates decreased, and large MV complexes increased in those SFO and VO maintained in culture for a prolonged period of time (8–9 hours). A slight to moderate vacuolization was present in the cytoplasm of SFO. Only a slight vacuolization was present in VO, whereas vacuoles were almost completely absent in CO. Amount and density of cortical granules (CG) appeared abnormally reduced in SFO and VO, irrespective of the protocol applied.ConclusionsEven though, both slow freezing and vitrification ensured a good overall preservation of the oocyte, we found that: 1) prolonged culture activates an intracellular membrane “recycling” that causes the abnormal transformation of the membranes of the small MV complexes and of SER into larger rounded vesicles; 2) vacuolization appears as a recurrent form of cell damage during slow freezing and, at a lesser extent, during vitrification using a closed device; 3) premature CG exocytosis was present in both SFO and VO and may cause zona pellucida hardening.