Sperm were isolated from the semen of oligozoospermic (less than 20 x 10(6) sperm/ml) and normospermic (greater than or equal to 20 x 10(6) sperm/ml) men in an in-vitro fertilization (IVF) programme. Oocytes from the female partners were inseminated with either 75 or 100 x 10(3) motile sperm and checked for fertilization after 16-20 h. A significant reduction in the overall fertilization rate of oocytes was seen for the oligozoospermic group compared to the normospermic group, at both insemination concentrations. In the oligozoospermic group, a fertilization rate of 31% (19/61) was achieved when oocytes were inseminated with 75 x 10(3) sperm, and 38% (9/24) when inseminated with 100 x 10(3) sperm. This compared with rates of 57% (397/696) and 64% (650/1018), respectively, for normospermic cases at both insemination concentrations. No evidence of fertilization was seen in 36% (4/11) and 67% (4/6) of oligozoospermic cases when 75 or 100 x 10(3) sperm were used, compared with values of 13% (17/133) and 9% (20/212), respectively, in normospermic cases. After excluding zero cases, the fertilization rate of oocytes for the oligozoospermic group (75%; 9/12) was similar to the normospermic group (70% 650/935) when 100 x 10(3) sperm were used. However, when 75 x 10(3) sperm were used, the fertilization rate for the oligozoospermic group (41%; 19/46) was significantly lower than that of the normospermic group (62%; 397/645). Following the transfer of embryos into the female partner, clinical pregnancies were diagnosed in 2/7 (29%) oligozoospermic cases and 27/267 (10%) normospermic cases.(ABSTRACT TRUNCATED AT 250 WORDS)

A total of 101 multipronuclear oocytes (7.4% of fertilizations) were retrospectively identified in this in-vitro fertilization programme. The use of a manual syringe suction system, instead of an electric pump, to aspirate follicles, was associated with a significant increase in the proportion of oocytes with fractured zonae pellucidae (P less than 0.001), a lower normal fertilization rate (P less than 0.05) and a higher proportion of multipronuclear fertilizations (P less than 0.001). Irrespective of the mode of follicular aspiration, significantly more multipronuclear fertilizations occurred following stimulation with a combination of clomiphene and human menopausal gonadotrophin, than after clomiphene alone (P less than 0.05). It was concluded that the aspiration pressures, created by syringe suction, were more likely to rupture the zona pellucida of some oocytes, while in others it predisposed to an increased multipronuclear fertilization rate.

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