RESUMO
<p><b>OBJECTIVE</b>To determine the optimal fertilization method for primary infertility patients without definite causes undergoing in vitro fertilization and embryos transfer (IVF-ET).</p><p><b>METHODS</b>A total of 321 IVF-ET cycles for primary infertility without definite causes were divided into two groups, namely group A with infertility period ≥ 5 years (165 cycles) and group B with infertility period <5 years (156 cycles). Each group was further divided into IVF, ICSI, and partial ICSI subgroups. The fertilization rate, incidence of low fertilization rate and clinical pregnancy rate were analyzed.</p><p><b>RESULTS</b>The fertilization rate of IVF in group A was 67.5%, significantly lower than that of ICSI and partial ICSI in the same group (82.0% and 77.7% respectively) and that in IVF control group (76.3%, P<0.05). The incidence of low fertilization rate of IVF in group A was 33.3%, significantly lower than that of ICSI and partial ICSI (8.3% and 15.8%, P<0.05); in group B, the incidence of low fertilization rate of IVF was 12.3%, significantly lower than that of IVF in group A but showed no significant differences from that of ICSI and partial ICSI in group B (P>0.05). In group A, IVF resulted in a significantly lower clinical pregnancy rate (21.1%) than ICSI (43.3%, P<0.05), half ICSI (40.0%, P<0.05), IVF in the control group (48%, P<0.05), and IVF in group B (50.0%, P<0.05).</p><p><b>CONCLUSION</b>ICSI treatment can increase the fertilization rate in IVF-ET cycles in patients with primary infertility for unknown causes, and may improve the clinical outcome of patients with long infertility period.</p>