BACKGROUND:The recent development of a computer-assisted polarization microscopy system (Polscope) with which the meiotic spindle can be visualized in living oocytes on the basis of its birefringence permits analysis of the meiotic spindles of oocytes subjected to ICSI. Previous studies have shown that the meiotic spindle is not always aligned with the ®rst polar body (PB) in metaphase II human oocytes prepared for ICSI. In the present study, the relationship between the degree of meiotic spindle deviation from the ®rst PB location and ICSI outcome was analysed. METHODS: Oocytes were divided into four groups according to the angle of meiotic spindle deviation from the PB position. The angle of deviation was 0±5°, 6±45°, 46±90°and >90°for groups I to IV respectively. RESULTS: The rates of normal [2 pronuclei (PN)] and abnormal (1PN or >2PN) fertilization did not differ between groups I, II and III. However, the rate of normal fertilization was lower among oocytes in which the meiotic spindle deviation angle was >90°; this led to an increased proportion of tripronucleated zygotes that failed to extrude the second PB. When embryos developed from normally fertilized oocytes were evaluated on day 3 after ICSI, no relationship was found between the angle of meiotic spindle deviation and embryo quality. The meiotic spindle was not detected in only 9% of oocytes, and these showed a higher incidence of fertilization and cleavage abnormalities than did oocytes in which the spindle was detected. When oocytes at metaphase I after cumulus oophorus and corona radiata removal were matured in vitro, the meiotic spindle was detected in 53.8% of those that reached metaphase II. In these in-vitro-matured oocytes the meiotic spindle was always aligned with the ®rst PB, suggesting that misalignment seen in those oocytes matured in vivo resulted from PB displacement during manipulations for cumulus and corona removal. CONCLUSION: High degrees of misalignment between the meiotic spindle and the ®rst PB predict an increased risk of fertilization abnormalities. However, when normal fertilization had occurred, the cleavage potential of embryos developing from such oocytes was not impaired. These ®ndings facilitate the selection of oocytes for ICSI in situations when the creation of supernumerary embryos is to be avoided.Key words: ICSI/meiotic spindle/oocyte quality/polar body/Polscope Introduction The orientation of the injection channel and the sperm deposition site during ICSI are usually chosen with regard to the position of the ®rst polar body, assuming that the meiotic spindle with metaphase chromosomes is located in a nearby region of the oocyte cytoplasm. However, recent observations made with the use of a novel orientation-independent polarized microscopy system (Polscope), coupled with image processing software enabling the visualization of meiotic spindles in living oocytes, have shown that the ®rst polar body position does not predict accurately the location of the meiotic spindle in
The current techniques of oocyte freezing and thawing inevitably cause meiotic spindle destruction. All spindles observed in thawed oocytes result from post-thaw reconstruction.
Vitrification appears to be a viable method for the cryopreservation of human metaphase II (MII) oocytes, but concerns regarding the concentration of cryoprotectants used during vitrification have been raised. In an attempt to circumvent this potential problem, the majority of protocols are carried out at room temperature. Exposing oocytes to temperatures below 37 degrees C, however, leads to rapid microtubule depolymerization. Polarized light microscopy was used to measure meiotic spindle retardance following exposure to cryoprotectants and vitrification in human and mouse oocytes. To quantify the extent of depolymerization, spindle retardance was determined before and after each treatment. Exposure to vitrification and warming solutions at room temperature (21-22 degrees C) caused the spindle of mouse MII oocytes to depolymerize. In contrast, no measurable changes in the meiotic spindle were detected by maintaining the temperature at 37 degrees C during the exposure regimen. By carrying out the entire vitrification and warming procedure at 37 degrees C, the spindle was also unaffected. Comparable results were obtained with vitrification of human MII oocytes at 37 degrees C. Analysis of sibling human oocytes demonstrated that slow freezing, in contrast to vitrification, was unable to preserve the meiotic spindle. Using a vitrification protocol employing 37 degrees C impacts negligibly on the meiotic spindle. Thus, fertilization can proceed without having to await spindle reformation.
Over the last two decades, easier and less expensive stimulation treatments have been largely replaced by more complex and more demanding protocols. Since the mid-nineties, long-term gonadotrophin-releasing hormone agonist stimulation protocols have been widely used. Such lengthy expensive regimens are not free from short- and long-term risks and complications. Mild stimulation protocols reduce the mean number of days of stimulation, the total amount of gonadotrophins used and the mean number of oocytes retrieved. The proportion of high quality and euploid embryos seems to be higher compared with conventional stimulation protocols and the pregnancy rate per embryo transfer is comparable. Moreover, the reduced costs, the better tolerability for patients and the less time needed to complete an IVF cycle make mild approaches clinically and cost-effective over a given period of time. However, further prospective randomized studies are needed to compare cumulative pregnancy rates between the two protocols. Natural cycle IVF, with minimal stimulation, has been recently proposed as an alternative to conventional stimulation protocols in normo- and poor responder patients. Although acceptable results have been reported, further large prospective randomized studies are needed to better evaluate the efficacy of these minimal regimens compared with conventional stimulation approaches.
Italian legislation regarding reproductive medicine limits the number of embryos transferred per attempt to three. Thus, in order to achieve pregnancy, more IVF cycles may be required, generating a need for methods of ovarian stimulation with fewer side effects. The gonadotrophin-releasing hormone (GnRH) antagonists have several advantages in this respect, but there is a debate regarding a possible lower pregnancy rate from resulting cycles. This study evaluated the clinical applicability of GnRH antagonists for ovarian stimulation in young women undergoing intracytoplasmic sperm injection (ICSI) in which only three oocytes can be fertilized. The 200 women treated with GnRH antagonist had a significantly shorter stimulation and lower gonadotrophin consumption, oestradiol concentration, total and mature oocyte recovery as compared with 200 matched controls treated with GnRH agonist. No differences were found between the groups in the number of normal zygotes, total cleaved, transferred and high quality embryos, or in the clinical outcomes. Thus, the previously reported lower pregnancy rate in GnRH antagonist cycles may be related to the oocyte characteristics. Finally, under conditions of oocyte number restriction, the GnRH antagonist-based cycles may be proposed as an efficacious, safe and minimally invasive alternative to GnRH agonist in a standard long protocol.
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