Maturation in vitro of human oocytes from unstimulated cycles: selection of the optimal day for ovum retrieval based on follicular size

The potential use of immature oocytes for in-vitro fertilization (IVF) requ ires the conditions for successful maturation to be defined. This study foc used on the day of oocyte retrieval. The selection of a dominant follicle m ay induce endocrine changes in the remaining cohort that may be detrimental to their subsequent fertilization and embryonic development. Natural cycle s in volunteer donors were followed by measurement of serum oestradiol and by vaginal ultrasound, starting on day 3 of the cycle. Cycles were randomly allocated to one of two groups: group 1 (n = 10), in which follicles were aspirated before the leading follicle was 10 mm in diameter; and group 2 (n = 9), in which follicles were aspirated when a dominant follicle was clear ly visible with diameter >10 mm, Oocytes were cultured in vitro to metaphas e II (MII) stage, donated, and inseminated by intracytoplasmic sperm inject ion (ICSI) with husband's spermatozoa. Those that became fertilized within 24 h were further co-cultured in autologous endometrial epithelial cells up to the blastocyst stage, and cryopreserved. There was a significantly (P < 0.05) increased rate of oocyte retrieval in group 1 (70.8% of aspirated fo llicles) compared with group 2 (50.5%), Maturation to MII and fertilization were similar between the groups. However, development to blastocyst stage was significantly (P < 0.05) higher in group I embryos (56.5%) compared wit h group 2 (35.7%). There was a positive correlation (r(2) = 0.1978) between the appearance of the cumulus cells and the ability to develop to blastocy st stage when both parameters were analysed in group 1, whereas no such cor relation was found in group 2, In conclusion, our data suggest the importan ce of retrieving immature oocytes before follicular selection, and define t he conditions for the first stage in the use of immature oocytes, Further s tages must be defined before this technique ran be used clinically.