Abstract: AIM: To investigate and compare the therapeutic effect of letrozole on abnormal ovulation, and to investigate its indication and side effect.METHODS: 313 cases of abnormal ovulation who were treated for 871 treatment cycles were divided into 4 groups:anovulia without PCOS grouP( A) , PCOS grouP( B) , ovule ovulation( C) and LUFS ( D).They took letrozole 2.5 mg q.d.×5 d from menstruation stage 5th day and added HMG later.They were injected HCG 1 000 IU when average diameter of dominant follicle ≥18 μm or LH( +) in urine.The ovulation rates, pregnancy rates and abortion rates were compared among 4 groups.RESULTS: There were several cycles canceled in PCOS grouP( B) because there was OHSS or no dominant follicle.Dominant follicles rates were lower in grouPB than others.MFD was shorter in grouPC than others.The amount of MFD ≥15mm was more in grouPB than others.Pregnancy rates were higher for sinus ovarian follicle ≤8/side and less for MFD ≥15 mm.Early abortion rate was the highest in grouPC.All patients had bradymenorrhea, with 7 cycles in some patients having light gastrointestinal side effect.CONCLUSION: Letrozole can treat abnormal ovulation such as anovulia without PCOS.PCOS and LUFS can not improve the follicular development of ovule ovulation.The amount of sinus ovarian follicle before stimulated follicle can predict the sensitiveness of letrozole for PCOS.The time of stimulating follicle was best for 7 -13 days.There was slight side effect for letrozole.

Key words: letrozole, abnormal ovulation, polycystic ovarian syndrome, luteinized unruptured follicle syndrome