Spermatozoa selection at high magnification before intracytoplasmic sperm injection seems to be positively associated with pregnancy rates after day 3 embryo transfers. The aim was to demonstrate an association between the presence of vacuoles in sperm nuclei and the competence of embryos to develop to day 5. Grading of spermatozoa at x 6000-x 12,500 magnification: grade I, no vacuoles; grade II, or=1 large vacuole; grade IV, large vacuoles with other abnormalities. The outcome of embryo development in a group of 25 patients after sibling oocyte injection with the four different grades of spermatozoa showed no significant difference in embryo quality up to day 3. However, the occurrence of blastocyst formation was 56.3 and 61.4% with grade I and II spermatozoa respectively, compared with 5.1% with grade III and 0% with grade IV respectively (P < 0.001). Spermatozoa selection at high magnification using Nomarski interference contrast is useful to identify more precisely the size and the number of nuclear vacuoles that greatly exert a negative effect on embryo development to the blastocyst stage. These observations confirm previous studies pointing to possible 'early and late paternal effects', both of which may have an impact on early embryonic development.

Our results showed that survival rates in cryopreserved expanded blastocysts could be improved by reducing the fluid content. This was presumably because mechanical damage caused by ice crystal formation was avoided. These observations should be considered when establishing a strategy and a protocol for cryopreservation of day 5 embryos.

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Artificial opening of the zona pellucida after warming of vitrified blastocysts significantly improved the rate of transfers with hatched blastocysts and the implantation and pregnancy rates. The percentage of blastocysts that survived the HS vitrification procedure and were available for embryo transfer is related to their previous developmental quality.

The aim of this work was to evaluate the relationship between follicular size at the time of oocyte retrieval, and the subsequent oocyte competence to be fertilized and to develop in vitro. All the obtained oocytes were classified according to the corresponding volume of aspirated follicular fluid. Aspirated volume of follicular fluid <2 ml corresponded to a follicular diameter <16 mm and constituted the small size group. Volume of follicular fluid from 2 to 6 ml corresponded to a diameter from 16 to 23 mm and constituted the medium size group. The large size group contained follicles with diameter >23 mm and corresponded to an aspirated volume of follicular fluid of >6 ml. A progressive and significant increase in the rates of oocytes with a first polar body was observed from the small size group to the other groups and from the medium to the large size group: 75.3, 85.9 and 95.3% respectively. After classical in-vitro fertilization (IVF), significantly better rates of fertilization and development were obtained in the medium size group compared to the two other groups. Moreover, a positive relationship was observed between follicular diameter and rates of embryos scored as 'good' when oocytes were fertilized by intracytoplasmic sperm injection (ICSI). These results demonstrated that follicular size is positively related to the oocyte ability to be fertilized and to develop. Although oocytes from small follicles gave lower percentages of development probably due to partial oocyte incompetence, they allowed an increase in the total number of embryos scored as 'good'.