HUMAN OOCYTE CYTOMETRY AND FERTILIZATION RATE AFTER SUBZONAL INSEMINATION

The cytometry of 545 oocytes was evaluated during subzonal inseminatio n (SUZI; 85 attempts), on day 0 (egg retrieval and SUZI), day 1 and da y 2 (embryo transfer). On day 0, the egg and oolemma diameters (mean /- SD) were 164.0 +/- 19.6 mu m and 114.2 +/- 16.8 gamma 5m respective ly. The zona thickness was 17.8 +/- 13.4 mu m and correlated with the oolemma diameter (r = 0.24, p < 0.001). The fertilisation rate was sig nificantly lower for the smaller oocytes (less than 108 mu m diameter) compared with the larger oocytes (over 108 mu m) (9.8% vs 21.2% respe ctively; p < 0.05). There was little variation in oocyte diameter acco rding to nuclear status. However, oocyte diameter increased significan tly between day 0 and day 1 (p < 0.001) for both fertilised and unfert ilised oocytes. Six different indications for SUZI were investigated i n detail: three with non-specific (normal and subnormal sperm with in vitro fertilization failure, oligoasthenospermia) and three with speci fic sperm defects (flagellar dyskinesia, absence of outer dynein arms, antisperm antibodies). Oocytes from the non-specific defect groups ha d significantly smaller diameters than the others (p < 0.05). The mean fertilisation rate was related to the mean oolemma diameter for the g roups with non-specific sperm defects and the group lacking dynein arm s (LODA) (r = 0.91, p < 0.05). Eggs from the groups of patients with L ODA and those with antisperm antibodies had thicker zona pellucida tha n others (p < 0.05). These findings suggest that in addition to nuclea r criteria of maturity, the growth of oocytes is an important factor f or fertilising ability. Insufficient development of the ooplasm may co ntribute to fertilisation failure, particularly when sperm with functi onal defects are used. In contrast, a thick zona pellucida may prevent sperm with specific anomalies such as LODA or antisperm antibodies fr om penetrating into the perivitelline space.