OBJECTIVETo determine the optimal fertilization method for primary infertility patients without definite causes undergoing in vitro fertilization and embryos transfer (IVF-ET).

METHODSA 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.

RESULTSThe 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).

CONCLUSIONICSI 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.